[IPSEC] esp: Remove NAT-T checksum invalidation for BEET

I pointed this out back when this patch was first proposed but it looks like
it got lost along the way.

The checksum only needs to be ignored for NAT-T in transport mode where
we lose the original inner addresses due to NAT.  With BEET the inner
addresses will be intact so the checksum remains valid.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/esp4.c

@@ -261,8 +261,7 @@ static int esp_input(struct xfrm_state *x, struct sk_buff *skb)
 		 *    as per draft-ietf-ipsec-udp-encaps-06,
 		 *    section 3.1.2
 		 */
-		if (x->props.mode == XFRM_MODE_TRANSPORT ||
-		    x->props.mode == XFRM_MODE_BEET)
+		if (x->props.mode == XFRM_MODE_TRANSPORT)
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
 	}