IB/ipath: Fix PSN of send WQEs after an RDMA read resend

The PSN of the first packet after an RDMA read is based on the size of
the RDMA read request. This is calculated correctly for the WQE sent
after the first request message but not on subsequent requests if the
RDMA read is resent.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>