net: airoha: add RCU lock around dev_fill_forward_path

net: airoha: add RCU lock around dev_fill_forward_path

Since 0417adf367a0 ("ppp: fix race conditions in ppp_fill_forward_path")
dev_fill_forward_path() should be called with RCU read lock held. This
fix was applied to net, while the Airoha flowtable commit was applied to
net-next, so it hadn't been an issue until net was merged into net-next.

Fixes: a8bdd935d1dd ("net: airoha: Add wlan flowtable TX offload")
Signed-off-by: Qingfang Deng <dqfext@gmail.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260320094315.525126-1-dqfext@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>