mac80211: add led_trigger_blink{_oneshot}()

mac80211: add led_trigger_blink{_oneshot}()

When led support is deactivated in the kernel and
CPTCFG_BACKPORT_BUILD_LEDS is set mac80211 references
led_trigger_blink_oneshot() but it is not declared anywhere.

This fixes the following build error:
net/mac80211/led.c: In function 'ieee80211_led_rx':
net/mac80211/led.c:25:2: error: implicit declaration of function 'led_trigger_blink_oneshot' [-Werror=implicit-function-declaration]

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39530 3c298f89-4303-0410-b956-a3cf2f4a3e73