cfg80211: rename cfg80211_drv_mutex to cfg80211_mutex

cfg80211_drv_mutex is protecting more than the driver list,
this renames it and documents what its currently supposed to
protect.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --cc net/wireless/core.c
Simple merge

diff --cc net/wireless/core.h
Simple merge

diff --cc net/wireless/nl80211.c
Simple merge

diff --cc net/wireless/reg.c
Simple merge