Keep the Channel in clients receivers & senders

Channel contains the Arc<ChannelInner> so that
```rust
let streaming_stuff = Client::new(init_channel()).some_call();
```
does not die due to channel being dropped at the end of the line.

src/call/client.rs

@@ -129,7 +129,12 @@ impl Call {
                 tag,
             )
         });
-        Ok(ClientUnaryReceiver::new(call, cq_f, method.resp_de()))
+        Ok(ClientUnaryReceiver::new(
+            call,
+            cq_f,
+            method.resp_de(),
+            channel,
+        ))
     }
 
     pub fn client_streaming<Req, Resp>(
@@ -151,11 +156,12 @@ impl Call {
         });
 
         let share_call = Arc::new(SpinLock::new(ShareCall::new(call, cq_f)));
-        let sink = ClientCStreamSender::new(share_call.clone(), method.req_ser());
+        let sink = ClientCStreamSender::new(share_call.clone(), method.req_ser(), channel);
         let recv = ClientCStreamReceiver {
             call: share_call,
             resp_de: method.resp_de(),
             finished: false,
+            _channel_keepalive: channel.clone(),
         };
         Ok((sink, recv))
     }
@@ -189,7 +195,12 @@ impl Call {
             grpc_sys::grpcwrap_call_recv_initial_metadata(call.call, ctx, tag)
         });
 
-        Ok(ClientSStreamReceiver::new(call, cq_f, method.resp_de()))
+        Ok(ClientSStreamReceiver::new(
+            call,
+            cq_f,
+            method.resp_de(),
+            channel,
+        ))
     }
 
     pub fn duplex_streaming<Req, Resp>(
@@ -216,8 +227,8 @@ impl Call {
         });
 
         let share_call = Arc::new(SpinLock::new(ShareCall::new(call, cq_f)));
-        let sink = ClientDuplexSender::new(share_call.clone(), method.req_ser());
-        let recv = ClientDuplexReceiver::new(share_call, method.resp_de());
+        let sink = ClientDuplexSender::new(share_call.clone(), method.req_ser(), channel);
+        let recv = ClientDuplexReceiver::new(share_call, method.resp_de(), channel);
         Ok((sink, recv))
     }
 }
@@ -230,14 +241,21 @@ pub struct ClientUnaryReceiver<T> {
     call: Call,
     resp_f: BatchFuture,
     resp_de: DeserializeFn<T>,
+    _channel_keepalive: Channel,
 }
 
 impl<T> ClientUnaryReceiver<T> {
-    fn new(call: Call, resp_f: BatchFuture, resp_de: DeserializeFn<T>) -> ClientUnaryReceiver<T> {
+    fn new(
+        call: Call,
+        resp_f: BatchFuture,
+        resp_de: DeserializeFn<T>,
+        _channel_keepalive: &Channel,
+    ) -> ClientUnaryReceiver<T> {
         ClientUnaryReceiver {
             call,
             resp_f,
             resp_de,
+            _channel_keepalive: _channel_keepalive.clone(),
         }
     }
 
@@ -276,6 +294,7 @@ pub struct ClientCStreamReceiver<T> {
     call: Arc<SpinLock<ShareCall>>,
     resp_de: DeserializeFn<T>,
     finished: bool,
+    _channel_keepalive: Channel,
 }
 
 impl<T> ClientCStreamReceiver<T> {
@@ -326,15 +345,21 @@ pub struct StreamingCallSink<Req> {
     sink_base: SinkBase,
     close_f: Option<BatchFuture>,
     req_ser: SerializeFn<Req>,
+    _channel_keepalive: Channel,
 }
 
 impl<Req> StreamingCallSink<Req> {
-    fn new(call: Arc<SpinLock<ShareCall>>, req_ser: SerializeFn<Req>) -> StreamingCallSink<Req> {
+    fn new(
+        call: Arc<SpinLock<ShareCall>>,
+        req_ser: SerializeFn<Req>,
+        _channel_keepalive: &Channel,
+    ) -> StreamingCallSink<Req> {
         StreamingCallSink {
             call,
             sink_base: SinkBase::new(false),
             close_f: None,
             req_ser,
+            _channel_keepalive: _channel_keepalive.clone(),
         }
     }
 
@@ -490,17 +515,20 @@ impl<H: ShareCallHolder, T> ResponseStreamImpl<H, T> {
 #[must_use = "if unused the ClientSStreamReceiver may immediately cancel the RPC"]
 pub struct ClientSStreamReceiver<Resp> {
     imp: ResponseStreamImpl<ShareCall, Resp>,
+    _channel_keepalive: Channel,
 }
 
 impl<Resp> ClientSStreamReceiver<Resp> {
     fn new(
         call: Call,
         finish_f: BatchFuture,
         de: DeserializeFn<Resp>,
+        _channel_keepalive: &Channel,
     ) -> ClientSStreamReceiver<Resp> {
         let share_call = ShareCall::new(call, finish_f);
         ClientSStreamReceiver {
             imp: ResponseStreamImpl::new(share_call, de),
+            _channel_keepalive: _channel_keepalive.clone(),
         }
     }
 
@@ -528,12 +556,18 @@ impl<Resp> Stream for ClientSStreamReceiver<Resp> {
 #[must_use = "if unused the ClientDuplexReceiver may immediately cancel the RPC"]
 pub struct ClientDuplexReceiver<Resp> {
     imp: ResponseStreamImpl<Arc<SpinLock<ShareCall>>, Resp>,
+    _channel_keepalive: Channel,
 }
 
 impl<Resp> ClientDuplexReceiver<Resp> {
-    fn new(call: Arc<SpinLock<ShareCall>>, de: DeserializeFn<Resp>) -> ClientDuplexReceiver<Resp> {
+    fn new(
+        call: Arc<SpinLock<ShareCall>>,
+        de: DeserializeFn<Resp>,
+        _channel_keepalive: &Channel,
+    ) -> ClientDuplexReceiver<Resp> {
         ClientDuplexReceiver {
             imp: ResponseStreamImpl::new(call, de),
+            _channel_keepalive: _channel_keepalive.clone(),
         }
     }