nexthop: Add support for lwt encaps

Add support for NHA_ENCAP and NHA_ENCAP_TYPE. Leverages the existing code
for lwtunnel within fib_nh_common, so the only change needed is handling
the attributes in the nexthop code.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/nexthop.h

@@ -35,6 +35,9 @@ struct nh_config {
 		struct in6_addr	ipv6;
 	} gw;
 
+	struct nlattr	*nh_encap;
+	u16		nh_encap_type;
+
 	u32		nlflags;
 	struct nl_info	nlinfo;
 };