cfg80211: Add multiple scan plans for scheduled scan

Add the option to configure multiple 'scan plans' for scheduled scan.
Each 'scan plan' defines the number of scan cycles and the interval
between scans. The scan plans are executed in the order they were
configured. The last scan plan will always run infinitely and thus
defines only the interval between scans.
The maximum number of scan plans supported by the device and the
maximum number of iterations in a single scan plan are advertised
to userspace so it can configure the scan plans appropriately.

When scheduled scan results are received there is no way to know which
scan plan is being currently executed, so there is no way to know when
the next scan iteration will start. This is not a problem, however.
The scan start timestamp is only used for flushing old scan results,
and there is no difference between flushing all results received until
the end of the previous iteration or the start of the current one,
since no results will be received in between.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>