[IPSEC]: Fix uh->len when doing NATT with IP options.

I just noticed that the UDP header length in esp4_output() is incorrect
when IP options are present (in transport mode).  This patch fixes exactly
that.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@redhat.com>

net/ipv4/esp4.c

@@ -124,7 +124,7 @@ int esp_output(struct sk_buff **pskb)
 		uh = (struct udphdr *)esph;
 		uh->source = encap->encap_sport;
 		uh->dest = encap->encap_dport;
-		uh->len = htons((*pskb)->len + alen - sizeof(struct iphdr));
+		uh->len = htons((*pskb)->len + alen - iph->ihl*4);
 		uh->check = 0;
 
 		switch (encap->encap_type) {