RDMA/srpt: Add support for immediate data

Modify allocation of the non-SRQ receive queues such that immediate
data is aligned on a 512 byte boundary. That alignment is necessary
to pass the immediate data without copying to the block layer. When
receiving an SRP_CMD with immediate data, postpone the ib_post_recv()
call until target_execute_cmd() has finished. See also
srpt_release_cmd().

Cc: Sergey Gorenko <[email protected]>
Cc: Max Gurtovoy <[email protected]>
Cc: Laurence Oberman <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>

Author: bvanassche