16B Management Packets (L4=0x08) replace the BTH and DETH
of normal MAD packet packets with a header containing the
the source and destination queue pair numbers; fields that
were originally retrieved from the BTH/DETH are now populated
from this header as well as from the 16B LRH (e.g. pkey).

16B Management Packets are used as an optimized management
format on 16B fabrics.

These management packets have an opcode of IB_OPCODE_UD_SEND_ONLY,
a fixed 3Byte pad, and a header length of 24Bytes.

The decision as to when we send a management packet is based
upon either the source or destination queue pair number being
0 or 1.
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Don Hiatt <don.hiatt@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>