mac80211: inform drivers about the off-channel status on channel changes

For some drivers it can be useful to know whether the channel they're
supposed to switch to is going to be used for short off-channel work or
scanning, or whether the hardware is expected to stay on it for a while
longer. This is important for various kinds of calibration work, which
takes longer to complete and should keep some persistent state, even if
the channel temporarily changes.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 20d372e..c7027ef 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -625,11 +625,14 @@
  *	may turn the device off as much as possible. Typically, this flag will
  *	be set when an interface is set UP but not associated or scanning, but
  *	it can also be unset in that case when monitor interfaces are active.
+ * @IEEE80211_CONF_OFFCHANNEL: The device is currently not on its main
+ *	operating channel.
  */
 enum ieee80211_conf_flags {
 	IEEE80211_CONF_MONITOR		= (1<<0),
 	IEEE80211_CONF_PS		= (1<<1),
 	IEEE80211_CONF_IDLE		= (1<<2),
+	IEEE80211_CONF_OFFCHANNEL	= (1<<3),
 };