bnx2: Allow flexible VLAN tag settings.

Negotiate with boot code and ASF firmware to see if it can
support keeping VLAN tags in the RX packets.  If supported
by firmware, the VLAN tag will be kept in the RX packet
unless VLAN acceleration is registered.

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