rtnetlink: add RTNH_F_EXTERNAL flag for fib offload

Add new RTNH_F_EXTERNAL flag to mark fib entries offloaded externally, for
example to a switchdev switch device.
Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/rtnetlink.h

@@ -334,6 +334,7 @@ struct rtnexthop {
 #define RTNH_F_DEAD		1	/* Nexthop is dead (used by multipath)	*/
 #define RTNH_F_PERVASIVE	2	/* Do recursive gateway lookup	*/
 #define RTNH_F_ONLINK		4	/* Gateway is forced on link	*/
+#define RTNH_F_EXTERNAL		8	/* Route installed externally	*/
 
 /* Macros to handle hexthops */