IB/ipath: Fix SLID generation for RC/UC QPs when LMC > 0

The code to set the source LID in the sent LRH was not setting the low
bits if LMC != 0 for RC/UC QPs.

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