IB/mad: Change slid in RMPP recv from 16 to 32 bits

MAD RMPP contains slid field which is 16 bits in
length, increase it to 32 bits.

Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Don Hiatt <don.hiatt@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>