IB/srpt: Don't allow reordering of commands on wait list

If a receive I/O context is removed from the wait list and
srpt_handle_new_iu() fails to allocate a send I/O context then
re-adding the receive I/O context to the wait list can cause
reordering. Avoid this by only removing a receive I/O context
from the wait list after allocating a send I/O context succeeded.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>