Avoid gopacket/pcap import to ease builds

We want to avoid importing `gopacket/pcap`; it forces CGO_ENABLED=1,
which makes cross-compilation more challenging, which makes publishing
binaries more difficult.

fixes, when running `bin/build`:

```
vendor/github.com/gopacket/gopacket/pcap/pcap.go:30:22: undefined: pcapErrorNotActivated
```

fixes, when running acceptance tests:

```
../vendor/github.com/gopacket/gopacket/pcap/pcap_unix.go:35:10: fatal error: 'pcap.h' file not found
```

Signed-off-by: Brian Cunnie <[email protected]>

pcap/pcap.go

@@ -15,7 +15,6 @@ import (
 
 	"github.com/gopacket/gopacket"
 	"github.com/gopacket/gopacket/layers"
-	"github.com/gopacket/gopacket/pcap"
 	"github.com/gopacket/gopacket/pcapgo"
 	"golang.org/x/crypto/ssh"
 
@@ -286,18 +285,16 @@ func openPcapHandle(tcpdumpCmd string, session *ssh.Session, wg *sync.WaitGroup,
 	// The pcap handle can be created without blocking after readable exists.
 	out := make(chan gopacket.Packet)
 	go func() {
-		handle, err := pcap.OpenOfflineFile(readable)
+		ngReader, err := pcapgo.NewNgReader(readable, pcapgo.NgReaderOptions{}) // which NgReaderOptions should I set?
 		if err != nil {
 			cancel(openHandleError)
 			return
 		}
 
-		packetSource := gopacket.NewPacketSource(handle, layers.LayerTypeEthernet)
+		packetSource := gopacket.NewPacketSource(ngReader, layers.LayerTypeEthernet)
 
 		// Run a goroutine that will write packets to the channel
 		go func() {
-			defer handle.Close()
-
 			for packet := range packetSource.Packets() {
 				out <- packet
 			}