kernel: qca8k: fix host FDB on multi-CPU

kernel: qca8k: fix host FDB on multi-CPU

On qca8k multi-CPU-port setups (e.g. qca8337 with ports 0+6 as CPU),
bridging switch user ports that use different conduits can make the host
reachable only from the ports tied to the last-programmed CPU port.

Add a pending kernel patch which makes qca8k merge CPU/DSA-port FDB
programming, so host FDB entries end up on all relevant CPU ports.

Fixes: openwrt/openwrt#17891
Signed-off-by: Kevin Staley <glaciertablet@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21317
Signed-off-by: Robert Marko <robimarko@gmail.com>