Since these counters can only be read through debugfs, there's
very little point in maintaining them all the time. However,
even just making them depend on debugfs is pointless - they're
not normally used. Additionally a number of them aren't even
concurrency safe.

Move them under MAC80211_DEBUG_COUNTERS so they're normally
not even compiled in.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>