kernel: remove bridge offload hack

kernel: remove bridge offload hack

This patch initially introduced in 94b4da9b4aaded6ed8a5bd93bf38a7c92753fe68
breaks mvebu devices when using vlan filtering with kernel 5.15 or 6.1,
it was working ok in 5.10.

With this patch, frame that should exit untagged from the switch exit tagged.
Running 'tcpdump -Q out -evnnli eth1' (eth1 being the dsa interface)
- with the hack, frame is sent directly to the
destination port 4 with VID 2, so the switch leave the tag as instructed:
11:22:33:44:55:66 > 77:88:99:aa:bb:cc, Marvell EDSA ethertype 0xdada (Unknown), rsvd 0 0, mode From CPU, target dev 0, port 4, tagged, VID 2, FPri 0, ethertype ARP (0x0806), length 50: Ethernet (len 6), IPv4 (len 4), Request who-has 5.6.7.8 tell 1.2.3.4, length 28

- without the hack, frame is sent to the switch that
performs the forwarding decision and untagging:
11:22:33:44:55:66 > 77:88:99:aa:bb:cc, Marvell EDSA ethertype 0xdada (Unknown), rsvd 0 0, mode Forward, dev 1, port 0, tagged, VID 2, FPri 0, ethertype ARP (0x0806), length 50: Ethernet (len 6), IPv4 (len 4), Request who-has 5.6.7.8 tell 1.2.3.4, length 28

Removing this patch makes my Turris Omnia usable with vlan filtering,
ie wifi device can talk to wired device again.
Using kernel 5.15 some broadcast/multicast traffic is still leaked
(on a VLAN 2 access port I see tagged VLAN 3 frame),
using kernel 6.1 fixes that.

People needing the extra performance should try the bridger package.

Acked-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>