xfrm: Pass flowi_oif or l3mdev as oif to xfrm_dst_lookup

The commit referenced in the Fixes tag no longer changes the
flow oif to the l3mdev ifindex. A xfrm use case was expecting
the flowi_oif to be the VRF if relevant and the change broke
that test. Update xfrm_bundle_create to pass oif if set and any
potential flowi_l3mdev if oif is not set.

Fixes: 40867d74 ("net: Add l3mdev index to flow struct and avoid oif reset for port devices")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_policy.c

@@ -2593,12 +2593,14 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
 
 		if (xfrm[i]->props.mode != XFRM_MODE_TRANSPORT) {
 			__u32 mark = 0;
+			int oif;
 
 			if (xfrm[i]->props.smark.v || xfrm[i]->props.smark.m)
 				mark = xfrm_smark_get(fl->flowi_mark, xfrm[i]);
 
 			family = xfrm[i]->props.family;
-			dst = xfrm_dst_lookup(xfrm[i], tos, fl->flowi_oif,
+			oif = fl->flowi_oif ? : fl->flowi_l3mdev;
+			dst = xfrm_dst_lookup(xfrm[i], tos, oif,
 					      &saddr, &daddr, family, mark);
 			err = PTR_ERR(dst);
 			if (IS_ERR(dst))