Revert "kernel: revert ip6_tunnel use skb_vlan_inet_prepare() in __ip6_tnl_rcv()"

This reverts commit ee0b160.

A backport commit was missing which was backported upstream with
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v6.12.71&id=4ce768ac429ec1c2d4ba63a408fed454ed12b248

Link: https://lore.kernel.org/all/CANn89iL5ksZZCJr7SK9=4Sw6EejdOzr5_m6pBMM8RVtbLy_ACA@mail.gmail.com/

Signed-off-by: Goetz Goerisch <ggoerisch@gmail.com>
Link: openwrt/openwrt#22025
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

Author: GoetzGoerisch