Test tcp_rmem and tcp_wmem max values handling

[okt-sergeyn]

Inspired by Xilinx-CNS/onload#227

In sockapi-ts/sockopts/max_bufs.c (https://github.com/Xilinx-CNS/cns-sapi-ts/blob/main/sockapi-ts/sockopts/max_bufs.c#L205)
it is written:

    /*
     * Note: for TCP tcp_wmem and tcp_rmem should not be taken into
     * account here; they are used for dymanic TCP buffers adjustment
     * and do not limit SO_SNDBUF/SO_RCVBUF according to Linux manual.
     */

However, the test doesn't check that.
I suggest to extend tcp iterations of the test (or create another one, idk) and check that tcp_wmem[2] and tcp_rmem[2] do not limit SO_SNDBUF/SO_RCVBUF socket options.

See man 7 tcp

       tcp_rmem (since Linux 2.4)
...
              max    the  maximum size of the receive buffer used by each TCP socket.  This value does
                     not override the global net.core.rmem_max.  This is not used to limit the size of
                     the  receive  buffer  declared using SO_RCVBUF on a socket.