net: Add priority to packet_offload objects.

When we scan a packet for GRO processing, we want to see the most
common packet types in the front of the offload_base list.

So add a priority field so we can handle this properly.

IPv4/IPv6 get the highest priority with the implicit zero priority
field.

Next comes ethernet with a priority of 10, and then we have the MPLS
types with a priority of 15.

Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Suggested-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index 594163d..0602e91 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -469,10 +469,14 @@
  */
 void dev_add_offload(struct packet_offload *po)
 {
-	struct list_head *head = &offload_base;
+	struct packet_offload *elem;
 
 	spin_lock(&offload_lock);
-	list_add_rcu(&po->list, head);
+	list_for_each_entry(elem, &offload_base, list) {
+		if (po->priority < elem->priority)
+			break;
+	}
+	list_add_rcu(&po->list, elem->list.prev);
 	spin_unlock(&offload_lock);
 }
 EXPORT_SYMBOL(dev_add_offload);