If the nbd server stops receiving packets altogether we will get stuck
waiting for them to receive indefinitely as the tcp buffer will never
empty, which looks like a deadlock.  Fix this by setting the sk send
timeout to our configured timeout, that way if the server really
misbehaves we'll disconnect cleanly instead of waiting forever.
Reported-by: NDan Melnic <dmm@fb.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NJens Axboe <axboe@fb.com>