vlan: Disable MAC address setting

We should not implicitly do nothing with the mac address. Report a
failure to set the MAC address on a VLAN to the caller.

Change-Id: I01d9ed2db190a53bc20a0d537f067838a9a1e8e0
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/vlan_interface.cpp b/vlan_interface.cpp
index 1b4eaee..73de4e8 100644
--- a/vlan_interface.cpp
+++ b/vlan_interface.cpp
@@ -37,6 +37,12 @@
     emit_object_added();
 }
 
+std::string VlanInterface::mACAddress(std::string)
+{
+    log<level::ERR>("Tried to set MAC address on VLAN");
+    elog<InternalFailure>();
+}
+
 void VlanInterface::writeDeviceFile()
 {
     using namespace std::string_literals;