switch: make LED port_mask file write handler use kstrtoul() function

switch: make LED port_mask file write handler use kstrtoul() function

This patch changes swconfig_trig_port_mask_store() handler to utilize
kstrtoul() function instead of call to obsolete simple_strtoul(). Thanks
to this change, new handler takes less memory and makes port_mask special
file accept not only hexadecimal, but also decimal and octal numbers.

Signed-off-by: Michal Cieslakiewicz <michal.cieslakiewicz@wp.pl>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48774 3c298f89-4303-0410-b956-a3cf2f4a3e73