removing "union" from xio_rdma_task.

the "union" caused errors in transactions were rdma_read and rdma_write
where involved

Signed-off-by: Eyal Salomon <esalomon@mellanox.com>
missing flag on server

Signed-off-by: Eyal Salomon <esalomon@mellanox.com>
Adding support for message flag XIO_MSG_FLAG_SMALL_ZERO_COPY

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