udp: remove headers from UDP packets before queueing

Remove UDP transport headers before queueing packets for reception.
This change simplifies a follow-up patch to add MSG_PEEK support.

Signed-off-by: Sam Kumar <samanthakumar@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/udp.h b/include/net/udp.h
index d870ec1..a0b0da9 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -158,6 +158,15 @@
 void udp_set_csum(bool nocheck, struct sk_buff *skb,
 		  __be32 saddr, __be32 daddr, int len);
 
+static inline void udp_csum_pull_header(struct sk_buff *skb)
+{
+	if (skb->ip_summed == CHECKSUM_NONE)
+		skb->csum = csum_partial(udp_hdr(skb), sizeof(struct udphdr),
+					 skb->csum);
+	skb_pull_rcsum(skb, sizeof(struct udphdr));
+	UDP_SKB_CB(skb)->cscov -= sizeof(struct udphdr);
+}
+
 struct sk_buff **udp_gro_receive(struct sk_buff **head, struct sk_buff *skb,
 				 struct udphdr *uh);
 int udp_gro_complete(struct sk_buff *skb, int nhoff);