via-rhine: fix VLAN receive handling regression.

Because eth_type_trans() consumes ethernet header worth of bytes, a call
to read TCI from end of packet using rhine_rx_vlan_tag() no longer works
as it's reading from an invalid offset.

Tested to be working on PCEngines Alix board.

Fixes: 810f19bc

 ("via-rhine: add consistent memory barrier in vlan receive code.")
Signed-off-by: Andrej Ota <andrej@ota.si>
Acked-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>