tg3: Re-inline VLAN tags when appropriate

The tg3 driver is written so that VLAN tagged packets can be accepted,
even if CONFIG_VLAN_8021Q or CONFIG_VLAN_8021Q_MODULE is not defined.
(Think raw interfaces.)  If the device has ASF support enabled, the
firmware requires the driver to enable VLAN tag stripping.  If VLAN
tagging is not explicitly supported by the kernel and ASF is enabled,
the driver will have to reinject the VLAN tag back into the packet
stream.

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