mxrouterctl: Fix bug with inherited vlan interfaces

Currently, when a vlan interface is created on the host system (e.g.
with mxvlan) and moved to the mxrouter instance with interface(), it
gets deleted, because it is recogized visible as a vlan interface in the
router namespace but not configured via vlan().

Ignore existing vlan interfaces which are configured into the router
namespace via interface().

mxrouter/mxrouterctl

@@ -488,6 +488,7 @@ sub start {
 	}
 
 	my ($have_vlan)=read_active_vlans();
+	delete $have_vlan->{$_} for keys %$want_if;  # vlan interfaces created in main and moved via interaface()
 	my ($new_vlan,$del_vlan)=({},{},{},{});
 
 	for (keys %$want_vlan) {