mac80211_hwsim: Check idle state on TX

Track the idle state for hwsim radios and reject TX if mac80211 is
trying to transmit something when the radio is supposed to be idle. In
addition, do not deliver frames if the receiving radio is in the idle
state.

Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>