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: Peter Kosyh <p.kosyh@gmail.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/xfrm4_policy.c b/net/ipv4/xfrm4_policy.c
index 1705476..23883a4 100644
--- a/net/ipv4/xfrm4_policy.c
+++ b/net/ipv4/xfrm4_policy.c
@@ -108,6 +108,8 @@
 	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: