bnx2: Reinsert VLAN tag when necessary.

In certain cases when ASF or other management firmware is running, the
chip may be configured to always strip out the VLAN tag even when
VLAN acceleration is not enabled.  This causes some VLAN tagged
packets to be received by the host stack without any knowledge that
the original packet was VLAN tagged.

We fix this by re-inserting the VLAN tag into the packet when necessary.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>