kernel: fix fraglist GRO on linux 6.12

Merged segments had a broken skb network header offset.

Fixes: https://github.com/openwrt/openwrt/issues/19130
Signed-off-by: Felix Fietkau <[email protected]>

target/linux/generic/pending-6.12/680-net-fix-TCP-UDP-fraglist-GRO.patch

@@ -0,0 +1,35 @@
+From: Felix Fietkau <[email protected]>
+Date: Sat, 5 Jul 2025 13:44:10 +0200
+Subject: [PATCH] net: fix TCP/UDP fraglist GRO
+
+Since "net: gro: use cb instead of skb->network_header", the skb network
+header is no longer set in the GRO path.
+This breaks fraglist segmentation, which relies on ip_hdr()/tcp_hdr()
+to check for address/port changes.
+Fix this regression by selectively setting the network header for merged
+segment skbs.
+
+Fixes: 186b1ea73ad8 ("net: gro: use cb instead of skb->network_header")
+Signed-off-by: Felix Fietkau <[email protected]>
+---
+
+--- a/net/ipv4/tcp_offload.c
++++ b/net/ipv4/tcp_offload.c
+@@ -355,6 +355,7 @@ struct sk_buff *tcp_gro_receive(struct l
+ 		flush |= skb->ip_summed != p->ip_summed;
+ 		flush |= skb->csum_level != p->csum_level;
+ 		flush |= NAPI_GRO_CB(p)->count >= 64;
++		skb_set_network_header(skb, skb_gro_receive_network_offset(skb));
+ 
+ 		if (flush || skb_gro_receive_list(p, skb))
+ 			mss = 1;
+--- a/net/ipv4/udp_offload.c
++++ b/net/ipv4/udp_offload.c
+@@ -604,6 +604,7 @@ static struct sk_buff *udp_gro_receive_s
+ 					NAPI_GRO_CB(skb)->flush = 1;
+ 					return NULL;
+ 				}
++				skb_set_network_header(skb, skb_gro_receive_network_offset(skb));
+ 				ret = skb_gro_receive_list(p, skb);
+ 			} else {
+ 				skb_gro_postpull_rcsum(skb, uh,

target/linux/generic/pending-6.12/690-net-add-missing-check-for-TCP-fraglist-GRO.patch

@@ -22,5 +22,5 @@ Signed-off-by: Felix Fietkau <[email protected]>
  		flush |= skb->csum_level != p->csum_level;
 +		flush |= !pskb_may_pull(skb, skb_gro_offset(skb));
  		flush |= NAPI_GRO_CB(p)->count >= 64;
+ 		skb_set_network_header(skb, skb_gro_receive_network_offset(skb));
  
- 		if (flush || skb_gro_receive_list(p, skb))