netfilter: bridge: allow fragmentation of VLAN packets traversing a bridge

br_nf_dev_queue_xmit only checks for ETH_P_IP packets for fragmenting but not
VLAN packets. This results in dropping of large VLAN packets. This can be
observed when connection tracking is enabled. Connection tracking re-assembles
fragmented packets, and these have to re-fragmented when transmitting out. Also,
make sure only refragmented packets are defragmented as per suggestion from
Patrick McHardy.
Signed-off-by: Saikiran Madugula <hummerbliss@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/bridge/br_netfilter.c

@@ -788,15 +788,23 @@ static unsigned int br_nf_local_out(unsigned int hook, struct sk_buff *skb,
 	return NF_STOLEN;
 }
 
+#if defined(CONFIG_NF_CONNTRACK_IPV4) || defined(CONFIG_NF_CONNTRACK_IPV4_MODULE)
 static int br_nf_dev_queue_xmit(struct sk_buff *skb)
 {
-	if (skb->protocol == htons(ETH_P_IP) &&
+	if (skb->nfct != NULL &&
+	    (skb->protocol == htons(ETH_P_IP) || IS_VLAN_IP(skb)) &&
 	    skb->len > skb->dev->mtu &&
 	    !skb_is_gso(skb))
 		return ip_fragment(skb, br_dev_queue_push_xmit);
 	else
 		return br_dev_queue_push_xmit(skb);
 }
+#else
+static int br_nf_dev_queue_xmit(struct sk_buff *skb)
+{
+        return br_dev_queue_push_xmit(skb);
+}
+#endif
 
 /* PF_BRIDGE/POST_ROUTING ********************************************/
 static unsigned int br_nf_post_routing(unsigned int hook, struct sk_buff *skb,