owl-linux: update help text about linux kernel dependencies.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/owl-linux/Config.in

@@ -6,6 +6,8 @@ config BR2_PACKAGE_OWL_LINUX
 	help
 	  Linux kernel driver for the H&D Wireless SPB104 SD-card WiFi SIP.
 
+	  owl-linux requires the hidden kernel option WIRELESS_EXT enabled.
+
 	  http://linux.hd-wireless.se/bin/view/Linux/GettingStarted
 
 comment "owl-linux requires a Linux kernel"