When the noise floor limits are being bypassed because of strong
interference, sensitivity is also reduced.
In order to recover from this as quickly as possible, trigger a
long periodic calibration every second instead of every 30 seconds,
until the NF median is within limits again. This is especially important
if the interference lasts for a while, since it takes multiple clean
NF calibrations to bring the median back to normal.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>