xfrm: fix xfrm by MARK logic

While using xfrm by MARK feature in
2.6.34 - 2.6.35 kernels, the mark
is always cleared in flowi structure via memset in
_decode_session4 (net/ipv4/xfrm4_policy.c), so
the policy lookup fails.
IPv6 code is affected by this bug too.
Signed-off-by: NPeter Kosyh <p.kosyh@gmail.com>
Acked-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/xfrm4_policy.c

@@ -108,6 +108,8 @@ _decode_session4(struct sk_buff *skb, struct flowi *fl, int reverse)
 	u8 *xprth = skb_network_header(skb) + iph->ihl * 4;
 
 	memset(fl, 0, sizeof(struct flowi));
+	fl->mark = skb->mark;
+
 	if (!(iph->frag_off & htons(IP_MF | IP_OFFSET))) {
 		switch (iph->protocol) {
 		case IPPROTO_UDP:

net/ipv6/xfrm6_policy.c

@@ -124,6 +124,8 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
 	u8 nexthdr = nh[IP6CB(skb)->nhoff];
 
 	memset(fl, 0, sizeof(struct flowi));
+	fl->mark = skb->mark;
+
 	ipv6_addr_copy(&fl->fl6_dst, reverse ? &hdr->saddr : &hdr->daddr);
 	ipv6_addr_copy(&fl->fl6_src, reverse ? &hdr->daddr : &hdr->saddr);