Description: ipv4, ipv6: Fix handling of transhdrlen in __ip{,6}_append_data()
References:
Notes:
 carnil> Introduced in a32e0eec7042 ("l2tp: introduce L2TPv3 IP encapsulation support
 carnil> for IPv6"). Vulnerable versions: 3.5-rc1.
Bugs:
upstream: released (6.6-rc5) [9d4c75800f61e5d75c1659ba201b6c0c7ead3070]
6.7-upstream-stable: N/A "Fixed before branching point"
6.6-upstream-stable: N/A "Fixed before branching point"
6.1-upstream-stable: released (6.1.57) [f6a7182179c0ed788e3755ee2ed18c888ddcc33f]
5.10-upstream-stable: released (5.10.198) [96b2e1090397217839fcd6c9b6d8f5d439e705ed]
4.19-upstream-stable: released (4.19.296) [559d697c5d072593d22b3e0bd8b8081108aeaf59]
sid: released (6.5.8-1)
6.1-bookworm-security: released (6.1.64-1)
5.10-bullseye-security: released (5.10.205-1)
4.19-buster-security: released (4.19.304-1)