net: sched: cls_u32: Avoid memcpy() false-positive warning in u32_init_knode()

net: sched: cls_u32: Avoid memcpy() false-positive warning in u32_init_knode()

Syzbot reported a warning in u32_init_knode() [1].

Similar to commit 7cba18332e36 ("net: sched: cls_u32: Avoid memcpy()
false-positive warning") which addressed the same issue in u32_change(),
use unsafe_memcpy() in u32_init_knode() to work around the compiler's
inability to see into composite flexible array structs.

This silences the false-positive reported by syzbot:

  memcpy: detected field-spanning write (size 32) of single field
  "&new->sel" at net/sched/cls_u32.c:855 (size 16)

Since the memory is correctly allocated with kzalloc_flex() using
s->nkeys, this is purely a false positive and does not need a Fixes tag.

[1] https://syzkaller.appspot.com/bug?extid=d5ace703ed883df56e42

Reported-by: syzbot+d5ace703ed883df56e42@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/69a811b9.a70a0220.b118c.0019.GAE@google.com/T/
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Link: https://patch.msgid.link/20260309123917.402183-1-jiayuan.chen@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>