neighbor: Add protocol attribute

Similar to routes and rules, add protocol attribute to neighbor entries
for easier tracking of how each was created.

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

include/uapi/linux/neighbour.h

@@ -28,6 +28,7 @@ enum {
 	NDA_MASTER,
 	NDA_LINK_NETNSID,
 	NDA_SRC_VNI,
+	NDA_PROTOCOL,  /* Originator of entry */
 	__NDA_MAX
 };