package/busybox: support automatic module loading with mdev

A recently discussed on the mailing list:
http://lists.busybox.net/pipermail/buildroot/2016-February/154189.html

Our mdev configuration currently doesn't handle module loading. Fix that by:

- Telling mdev to run modprobe on hotplug events providing MODALIAS

- Adjust the init script to handle coldplug modalias events (E.G. modules
  for which the devices were already present before mdev was added as the
  hotplug handler). mdev -s should arguable handle this, but it doesn't.

Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/busybox/S10mdev

@@ -8,6 +8,8 @@ case "$1" in
 	echo "Starting mdev..."
 	echo /sbin/mdev >/proc/sys/kernel/hotplug
 	/sbin/mdev -s
+	# coldplug modules
+	find /sys/ -name modalias | xargs sort -u | xargs modprobe -abq
 	;;
   stop)
 	;;

package/busybox/mdev.conf

@@ -33,3 +33,6 @@ event[0-9]+	root:root 640 =input/
 mice		root:root 640 =input/
 mouse[0-9]	root:root 640 =input/
 ts[0-9]		root:root 600 =input/
+
+# load modules
+$MODALIAS=.*	root:root 660 @modprobe "$MODALIAS"