IB/hfi1: Validate PKEY for incoming GSI MAD packets

These are the use-cases where the pkey needs to be tested to see
if a packet needs to be dropped.

a) Check if pkey is not FULL_MGMT_P_KEY or LIM_MGMT_P_KEY,
   drop the packet as it's not part of the management partition.
   Self-originated packets are an exception.

b) If pkey index points to FULL_MGMT_P_KEY and LIM_MGMT_P_KEY is
   in the table, the packet is coming from a management node,
   and the receiving node is also a management node, so it is safe
   for the packet to go through.

c) If pkey index points to FULL_MGMT_P_KEY and LIM_MGMT_P_KEY is
   NOT in the table, drop the packet as LIM_MGMT_P_KEY should
   always be in the pkey table. It could be a misconfiguration.

d) If pkey index points to LIM_MGMT_P_KEY and FULL_MGMT_P_KEY is
   NOT in the table, it is safe for the packet to go through
   since a non-management node is talking to another non-managment
   node.

e) If pkey index points to LIM_MGMT_P_KEY and FULL_MGMT_P_KEY is in
   the table, drop the packet because a non-management node is
   talking to a management node, and it could be an attack.

For the implementation, these rules can be simplied to only checking
for (a) and (e). There's no need to check for rule (b) as
the packet doesn't need to be dropped. Rule (c) is not possible in
the driver as LIM_MGMT_P_KEY is always in the pkey table.

Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Sebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>