nexthop: Introduce to struct nh_grp_entry a per-type union

The values that a next-hop group needs to keep track of depend on the group
type. Introduce a union to separate fields specific to the mpath groups
from fields specific to other group types.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/nexthop.h

@@ -66,7 +66,12 @@ struct nh_info {
 struct nh_grp_entry {
 	struct nexthop	*nh;
 	u8		weight;
-	atomic_t	upper_bound;
+
+	union {
+		struct {
+			atomic_t	upper_bound;
+		} mpath;
+	};
 
 	struct list_head nh_list;
 	struct nexthop	*nh_parent;  /* nexthop of group with this entry */