The separate header file is not needed since none of the driver wrappers
include it anymore. Move the WLAN_STA_* definitions back to be together
with struct sta_info definition.
Instead of getting this via hostapd.h, include it as the first
non-system header file in all source code files in the same way as
used in all other files.
This makes it clearer which files are including header from src/common.
Some of these cases should probably be cleaned up in the future not to
do that.
In addition, src/common/nl80211_copy.h and wireless_copy.h were moved
into src/drivers since they are only used by driver wrappers and do not
need to live in src/common.
