bnxt_en: Do not use the CNP CoS queue for networking traffic.

The CNP CoS queue is reserved for internal RDMA Congestion Notification
Packets (CNP) and should not be used for a TC.  Modify the CoS queue
discovery code to skip over the CNP CoS queue and to reduce
bp->max_tc accordingly.  However, if RDMA is disabled in NVRAM, the
the CNP CoS queue can be used for a TC.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>