Merge branch 'net-fix-potential-crash-in-net-sched-cls_u32-c'

Eric Dumazet says:

====================
net: fix potential crash in net/sched/cls_u32.c

GangMin Kim provided a report and a repro fooling u32_classify().

Add skb_header_pointer_careful() variant of skb_header_pointer()
and use it in net/sched/cls_u32.c.

Later we can also use it in net/sched/act_pedit.c
====================

Link: https://patch.msgid.link/20260128141539.3404400-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>