asix: allow full size 8021Q frames to be received

commit 9dae31009b1a00d926c6fe032d5a88099620adc3 upstream.

asix driver drops 8021Q full size frames because it doesn't take into
account VLAN header size.

Tested on AX88772 adapter.

Signed-off-by: Eric Dumazet <edumazet@google.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Allan Chou <allan@asix.com.tw>
CC: Trond Wuellner <trond@chromium.org>
CC: Grant Grundler <grundler@chromium.org>
CC: Paul Stewart <pstew@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: no offset used in asix_rx_fixup()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>