In Ubuntu 18 systemd-networkd cnet search, remove unnecessary .network files.

These files are dynamically generated by udev rule for any ethernet
interface other than lo or ifbs, but we don't want them to pay attention
to any interface if we've already found the control net device.

clientside/tmcc/ubuntu18/emulab-networkd.sh

@@ -21,7 +21,8 @@ found=0
 while [ ! $found -eq 1 ]; do
     # If the control net iface was found, and it's not us, exit.
     if [ -e /run/cnet ]; then
-	echo "`date`: ${iface}: control net is not us" >>$LOGFILE 2>&1
+	echo "`date`: ${iface}: control net is not us, removing ${iface}.network" >>$LOGFILE 2>&1
+	rm -f /run/systemd/network/${iface}.network
 	exit 0
     fi
     #