gro: change the BUG_ON() in gro_pull_from_frag0()

[ Upstream commit cbe4136 ]

Replace the BUG_ON() which never fired with a DEBUG_NET_WARN_ON_ONCE()

$ scripts/bloat-o-meter -t vmlinux.1 vmlinux.2
add/remove: 2/2 grow/shrink: 1/1 up/down: 370/-254 (116)
Function                                     old     new   delta
gro_try_pull_from_frag0                        -     196    +196
napi_gro_frags                               771     929    +158
__pfx_gro_try_pull_from_frag0                  -      16     +16
__pfx_gro_pull_from_frag0                     16       -     -16
dev_gro_receive                             1514    1464     -50
gro_pull_from_frag0                          188       -    -188
Total: Before=22565899, After=22566015, chg +0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260122045720.1221017-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: edumazet

net/core/gro.c

@@ -386,7 +386,7 @@ static void gro_pull_from_frag0(struct sk_buff *skb, int grow)
 {
 	struct skb_shared_info *pinfo = skb_shinfo(skb);
 
-	BUG_ON(skb->end - skb->tail < grow);
+	DEBUG_NET_WARN_ON_ONCE(skb->end - skb->tail < grow);
 
 	memcpy(skb_tail_pointer(skb), NAPI_GRO_CB(skb)->frag0, grow);