Under congestion resulting in eager buffer overflow attempt to send
pre-emptive NAKs if header queue entries with TID errors are generated
and a valid header is present.  This prevents long timeouts and flow
restarts if a trailing set of packets are dropped due to eager
overflows.  Pre-emptive NAKs are currently only supported for RDMA
writes.
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>