With XENVIFROUTING on, no point in restarting DHCP when adding an entry,

since the vif foes not exist yet, and we call restartDHCP() again in
emulab-cnet after the container and vif exist. In fact, no point in
restarting DHCP when removing an entry, since by that time the vif is
gone and dhcpd does not seem to mind that anyway.

clientside/tmcc/linux/xen/libvnode_xen.pm

@@ -4339,7 +4339,15 @@ sub modDHCP($$$$$)
     }
 
     if ($doHUP) {
-        restartDHCP();
+	#
+	# When using XENVIFROUTING, no point in restarting for a new VM;
+	# the new vif does not exist yet. Instead, we do the restart in
+	# emulab-cnet which is called after the vif (container) is created.
+	# Ditto when removing, this is done in emulab-cnet.
+	#
+	if (!$VIFROUTING) {
+	    restartDHCP();
+	}
     }
 
     TBDebugTimeStamp("  releasing DHCP lock")