ipv4: Prepare for fib6_nh from a nexthop object

Convert more IPv4 code to use fib_nh_common over fib_nh to enable routes
to use a fib6_nh based nexthop. In the end, only code not using a
nexthop object in a fib_info should directly access fib_nh in a fib_info
without checking the famiy and going through fib_nh_common. Those
functions will be marked when it is not directly evident.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c
index ab06fd7..88807c1 100644
--- a/net/ipv4/fib_rules.c
+++ b/net/ipv4/fib_rules.c
@@ -147,9 +147,9 @@ static bool fib4_rule_suppress(struct fib_rule *rule, struct fib_lookup_arg *arg
 	struct net_device *dev = NULL;
 
 	if (result->fi) {
-		struct fib_nh *nh = fib_info_nh(result->fi, 0);
+		struct fib_nh_common *nhc = fib_info_nhc(result->fi, 0);
 
-		dev = nh->fib_nh_dev;
+		dev = nhc->nhc_dev;
 	}
 
 	/* do not accept result if the route does