udp: Add udp6_lib_lookup_skb and udp4_lib_lookup_skb

Add externally visible functions to lookup a UDP socket by skb. This
will be used for GRO in UDP sockets. These functions also check
if skb->dst is set, and if it is not skb->dev is used to get dev_net.
This allows calling lookup functions before dst has been set on the
skbuff.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/udp.h

@@ -269,6 +269,8 @@ struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
 struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
 			       __be32 daddr, __be16 dport, int dif,
 			       struct udp_table *tbl, struct sk_buff *skb);
+struct sock *udp4_lib_lookup_skb(struct sk_buff *skb,
+				 __be16 sport, __be16 dport);
 struct sock *udp6_lib_lookup(struct net *net,
 			     const struct in6_addr *saddr, __be16 sport,
 			     const struct in6_addr *daddr, __be16 dport,
@@ -278,6 +280,8 @@ struct sock *__udp6_lib_lookup(struct net *net,
 			       const struct in6_addr *daddr, __be16 dport,
 			       int dif, struct udp_table *tbl,
 			       struct sk_buff *skb);
+struct sock *udp6_lib_lookup_skb(struct sk_buff *skb,
+				 __be16 sport, __be16 dport);
 
 /*
  * 	SNMP statistics for UDP and UDP-Lite