Destroy v4 callback channel.

Signed-off-by: Srikrishan Malik <srimalik@in.ibm.com>
Mark the socket to be closed on client destroy.

Signed-off-by: Srikrishan Malik <srimalik@in.ibm.com>
Explicity initialize the chan mutex.

Signed-off-by: Srikrishan Malik <srimalik@in.ibm.com>