xfrm: fix xfrm child route lookup for packet offload

In current code, xfrm_bundle_create() always uses the matched
SA's family type to look up a xfrm child route for the skb.
The route returned by xfrm_dst_lookup() will eventually be
used in xfrm_output_resume() (skb_dst(skb)->ops->local_out()).

If packet offload is used, the above behavior can lead to
calling ip_local_out() for an IPv6 packet or calling
ip6_local_out() for an IPv4 packet, which is likely to fail.

This change fixes the behavior by checking if the matched SA
has packet offload enabled. If not, keep the same behavior;
if yes, use the matched SP's family type for the lookup.

Test: verified IPv6-in-IPv4 packets on Android device with
      IPsec packet offload enabled
Signed-off-by: Mike Yu <yumike@google.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_policy.c

@@ -2694,7 +2694,9 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
 			if (xfrm[i]->props.smark.v || xfrm[i]->props.smark.m)
 				mark = xfrm_smark_get(fl->flowi_mark, xfrm[i]);
 
+			if (xfrm[i]->xso.type != XFRM_DEV_OFFLOAD_PACKET)
 				family = xfrm[i]->props.family;
+
 			oif = fl->flowi_oif ? : fl->flowi_l3mdev;
 			dst = xfrm_dst_lookup(xfrm[i], tos, oif,
 					      &saddr, &daddr, family, mark);