Description: l2tp: missing lock when clearing sk_user_data can lead to NULL pointer dereference
References:
 https://bugzilla.redhat.com/show_bug.cgi?id=2134528
 https://lore.kernel.org/all/20220810102848.282778-1-jakub@cloudflare.com/t
 https://lore.kernel.org/all/20220815130107.149345-1-jakub@cloudflare.com/t
 https://lore.kernel.org/all/20220823101459.211986-1-jakub@cloudflare.com/t
 https://lore.kernel.org/all/20221114191619.124659-1-jakub@cloudflare.com/t
Notes:
Bugs:
upstream: released (6.1-rc6) [b68777d54fac21fc833ec26ea1a2a84f975ab035], released (6.1-rc7) [af295e854a4e3813ffbdef26dbb6a4d6226c3ea1]
6.1-upstream-stable: N/A "Fixed before branch point"
5.10-upstream-stable: released (5.10.166) [e34a965f771f1977f172593c73e373036c765724, 5b209b8c99d487a1c32983981bf3552980fda591]
4.19-upstream-stable: needed
sid: released (6.1.4-1)
6.1-bookworm-security: N/A "Fixed before branch point"
5.10-bullseye-security: released (5.10.178-1)
4.19-buster-security: needed