kernel: ip6_tunnel: fix NEXTHDR_FRAGMENT handling in ip6_tnl_parse_tlv_enc_lim()

In the Linux kernel, the following vulnerability has been resolved: ip6tunnel: fix NEXTHDRFRAGMENT handling in ip6tnlparsetlvenclim syzbot pointed out 1 that NEXTHDRFRAGMENT handling is broken. Reading fragoff can only be done if we pulled enough bytes to skb-head. Currently we might access...