vxlan: 'external' implies 'nolearning'

It doesn't make sense to use external control plane and fill internal FDB at
the same time. It's even an illegal combination for VXLAN-GPE.

Just switch off learning when 'external' is specified.
Signed-off-by: Jiri Benc <jbenc@redhat.com>

ip/iplink_vxlan.c

@@ -234,6 +234,7 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 			remcsumrx = 0;
 		} else if (!matches(*argv, "external")) {
 			metadata = 1;
+			learning = 0;
 		} else if (!matches(*argv, "noexternal")) {
 			metadata = 0;
 		} else if (!matches(*argv, "gbp")) {