ath9k_htc: Remove OP_ASSOCIATED variable

mac80211 stores the association state in ieee80211_bss_conf.
Use this and remove the local state, which is incorrect anyway
since it is stored globally and not on a per-VIF basis.

Restarting ANI and reconfiguration of HW beacon timers when a
scan run ends requires more work. This is handled by iterating
over the active interfaces.

Finally, remove the useless check for associated status in RX
processing.

Signed-off-by: Sujith Manoharan <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>