I was poking about in the National Semi 83820 driver, and I happened to notice that the chip supports vlan tag add/strip assist in hardware, but the driver wasn't making use of it.  This patch adds in the driver support to use the vlan tag add/remove hardware, and enables the drivers use of the kernel vlan hwaccel interface.
Signed-off-by: Neil Horman <nhorman@redhat.com>