bnxt_en: Return relevant error code when offload fails

The driver returns -ENOSPC when tc_can_offload() check fails. Since that
routine checks for flow parameters that are not supported by the driver,
we should return the more appropriate -EOPNOTSUPP.

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