xfrm: update flowi saddr in icmp_send if unset

otherwise xfrm_lookup will fail to find correct policy

Signed-off-by: Ulrich Weber <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/icmp.c

···
 		/* No need to clone since we're just using its address. */
 		rt2 = rt;
 
+		if (!fl.nl_u.ip4_u.saddr)
+			fl.nl_u.ip4_u.saddr = rt->rt_src;
+
 		err = xfrm_lookup(net, (struct dst_entry **)&rt, &fl, NULL, 0);
 		switch (err) {
 		case 0: