fastd: replace ifconfig by ip link set

fastd/fastd.conf

@@ -41,9 +41,9 @@ mtu 1406;
 status socket "/var/run/fastd.{{ site }}_{{ network }}.sock";
 
 on up "
-	ifconfig $INTERFACE down
+	ip link set $INTERFACE down
 	ip link set address {{ mac_address }} dev $INTERFACE
-	ifconfig $INTERFACE up
+	ip link set $INTERFACE up
 
 	batctl -m {{ bat_iface }} if add $INTERFACE
 ";