IB/ipath: Only increment SSN if WQE is put on send queue

If a send work request has immediate errors and is not put on the
send queue, we shouldn't update any of the QP state.

The increment of the SSN wasn't obeying this.

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