mac80211: rename scan_state to next_scan_state

Rename scan_state to next_scan_state to better reflect
what it is used for.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>