[ICMP]: Restore pskb_pull calls in receive function

Somewhere along the development of my ICMP relookup patch the header
length check went AWOL on the non-IPsec path.  This patch restores the
check.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index cbb5b9c..121d517 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -683,7 +683,8 @@
 		}
 	}
 
-	__skb_pull(skb, sizeof(*hdr));
+	if (!pskb_pull(skb, sizeof(*hdr)))
+		goto discard_it;
 
 	hdr = icmp6_hdr(skb);