separate the sliding window sn for response and request.
on bidirectional connections, rdma_read may queue requests.
therefore, response that was sent after request may arrive before
the request resulting in error with sliding window

Change-Id: Iee58a51ed7330f60561e0cec26e144b1363c30d5
Signed-off-by: Eyal Salomon <esalomon@mellanox.com>