cfg80211: add generic helper to check interface is running

Add a helper using wdev to check if interface is running. This
deals with both non-netdev and netdev interfaces. In struct
wireless_dev replace 'p2p_started' and 'nan_started' by
'is_running' as those are mutually exclusive anyway, and unify
all the code to use wdev_running().

Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>