IB/hfi1: Correctly process FECN and BECN in packets

A CA is supposed to ignore FECN bits in multicast, ACK, and CNP
packets. This patch corrects the behavior of the HFI1 driver in this
regard by ignoring FECNs in those packet types.

While fixing the above behavior, fix the extraction of the FECN and BECN
bits from the packet headers for both 9B and 16B packets.

Furthermore, this patch corrects the driver's response to a FECN in RDMA
READ RESPONSE packets. Instead of sending an "empty" ACK, the driver now
sends a CNP packet. While editing that code path, add the missing trace
for CNP packets.

Fixes: 88733e3b ("IB/hfi1: Add 16B UD support")
Fixes: f59fb9e0

 ("IB/hfi1: Fix handling of FECN marked multicast packet")
Reviewed-by: Kaike Wan <kaike.wan@intel.com>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>