platform: use translated VLAN flags

The internal VLAN flags were translated into the kernel VLAN flags but
finally the internal ones were passed to the kernel instead.

Reported-by: Julien Nabet <serval2412@yahoo.fr>

src/platform/nm-linux-platform.c

@@ -1742,7 +1742,7 @@ vlan_add (NMPlatform *platform, const char *name, int parent, int vlan_id, guint
 
 	rtnl_link_set_link (rtnllink, parent);
 	rtnl_link_vlan_set_id (rtnllink, vlan_id);
-	rtnl_link_vlan_set_flags (rtnllink, vlan_flags);
+	rtnl_link_vlan_set_flags (rtnllink, kernel_flags);
 
 	return add_object (platform, object);
 }