When running as a 4-addr station against an AP that has the 4-addr VLAN
interface and the main 3-addr AP interface bridged together, sometimes
frames originating from the station were looping back from the 3-addr AP
interface, causing the bridge code to emit warnings about receiving frames
with its own source address.
I'm not sure why this is happening yet, but I think it's a good idea to
drop all frames (except 802.1x/EAP frames) that do not match the configured
addressing mode, including 4-address frames sent to a 3-address station.
User test reports indicate that the problem goes away with this patch.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>