Add logic for saving measurement-reports from STAs.
This commit does not yet save the measurement-reports received from
clients but adds the necessary code to do so. Currently the codes can
only handle beacon-reports, but link measurements can be added to it in
the future.
It also adds the new config-key measurement_report_timeout which
controls how long measurements are saved upon they are received by a
STA.
Signed-off-by: David Bauer <mail@david-bauer.net>
