(legacy) remove illegal ifconfig tag, which might result in an interface address reset

more info : https://forum.opnsense.org/index.php?topic=1562.msg4811#msg4811

src/sbin/dhclient-script.ext

@@ -103,7 +103,6 @@ add_new_address() {
 		netmask $new_subnet_mask \
 		broadcast $new_broadcast_address \
 		$medium
-	$IFCONFIG $interface setfirst $new_ip_address
 
 	$LOGGER "New IP Address ($interface): $new_ip_address"
 	$LOGGER "New Subnet Mask ($interface): $new_subnet_mask"