RDS: IB: Remove the RDS_IB_SEND_OP dependency

This helps to combine asynchronous fastreg MR completion handler
with send completion handler.

No functional change.

Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>