IB/hfi1: Define 16B Management Packets

Add 16B Management Packet definition. This optimized packet
format replaces the ib_other_headers and BTH with a source
and destination QP number.

To support these packets we introduce struct opa_16b_mgmt
into the struct hfi1_16b_header.

This packet format is only used for MAD packets using the
IB_OPCODE_UD_SEND_ONLY opcode on QP0/1.

The original 16B implementation failed to use 16B management
packets so now we add their definition.

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>