images: add syntax declaration to macvlan.proto

travis-ci: success for images: add syntax declaration to macvlan.proto
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

images/macvlan.proto

+syntax = "proto2";
+
 message macvlan_link_entry {
 	required uint32	mode	= 1;
 	optional uint32 flags	= 2;