mac80211: make LED trigger names available early

The throughput trigger will require doing LED
classdev/trigger handling before register_hw(),
so drivers should have access to the trigger
names before it. If trigger registration fails,
this will still make the trigger name available,
but that's not a big problem since the default
trigger will the simply not be found.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>