nexthop: allow nexthop_mpath_fill_node() to be called without RTNL

nexthop_mpath_fill_node() will be potentially called
from contexts holding rcu_lock instead of RTNL.
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/all/ZdZDWVdjMaQkXBgW@shredder/Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/nexthop.h

@@ -317,7 +317,7 @@ static inline
 int nexthop_mpath_fill_node(struct sk_buff *skb, struct nexthop *nh,
 			    u8 rt_family)
 {
-	struct nh_group *nhg = rtnl_dereference(nh->nh_grp);
+	struct nh_group *nhg = rcu_dereference_rtnl(nh->nh_grp);
 	int i;
 
 	for (i = 0; i < nhg->num_nh; i++) {