[][Kernel][mt7986][hnat][Add processing of unexpected skb]

[Description]
Add processing of uninitialized mac header skb in HNAT to avoid crash.

[Release-log]
N/A


Change-Id: I7915ab5cb9c366728b70a6597ba06cb6f984e4a8
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6887447
1 file changed