ipv4: Prepare rtable for IPv6 gateway

To allow the gateway to be either an IPv4 or IPv6 address, remove
rt_uses_gateway from rtable and replace with rt_gw_family. If
rt_gw_family is set it implies rt_uses_gateway. Rename rt_gateway
to rt_gw4 to represent the IPv4 version.

Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.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 d73a6d6..ee53a91 100644
--- a/net/ipv4/xfrm4_policy.c
+++ b/net/ipv4/xfrm4_policy.c
@@ -97,8 +97,9 @@ static int xfrm4_fill_dst(struct xfrm_dst *xdst, struct net_device *dev,
 	xdst->u.rt.rt_flags = rt->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST |
 					      RTCF_LOCAL);
 	xdst->u.rt.rt_type = rt->rt_type;
-	xdst->u.rt.rt_gateway = rt->rt_gateway;
-	xdst->u.rt.rt_uses_gateway = rt->rt_uses_gateway;
+	xdst->u.rt.rt_gw_family = rt->rt_gw_family;
+	if (rt->rt_gw_family == AF_INET)
+		xdst->u.rt.rt_gw4 = rt->rt_gw4;
 	xdst->u.rt.rt_pmtu = rt->rt_pmtu;
 	xdst->u.rt.rt_mtu_locked = rt->rt_mtu_locked;
 	INIT_LIST_HEAD(&xdst->u.rt.rt_uncached);