[IPSEC]: Move ip_summed zapping out of xfrm6_rcv_spi

Not every transform needs to zap ip_summed.  For example, a pure tunnel
mode encapsulation does not affect the hardware checksum at all.  In fact,
every algorithm (that needs this) other than AH6 already does its own
ip_summed zapping.

This patch moves the zapping into AH6 which is in line with what IPv4 does.

Possible future optimisation: Checksum the data as we copy them in IPComp.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ah6.c

@@ -344,6 +344,8 @@ static int ah6_input(struct xfrm_state *x, struct sk_buff *skb)
 	    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 		goto out;
 
+	skb->ip_summed = CHECKSUM_NONE;
+
 	hdr_len = skb->data - skb_network_header(skb);
 	ah = (struct ip_auth_hdr *)skb->data;
 	ahp = x->data;

net/ipv6/xfrm6_input.c

@@ -97,7 +97,6 @@ int xfrm6_rcv_spi(struct sk_buff *skb, int nexthdr, __be32 spi)
 	memcpy(skb->sp->xvec + skb->sp->len, xfrm_vec,
 	       xfrm_nr * sizeof(xfrm_vec[0]));
 	skb->sp->len += xfrm_nr;
-	skb->ip_summed = CHECKSUM_NONE;
 
 	nf_reset(skb);