[change] If VPN link is unstable, wifi sessions are closed and opened all the time

[nemesifier]

I spotted this on a couple of instances: an unstable management VPN link fails often, wifi sessions are flagged as closed and then reopen, so in 1 day there's hundred of wifi sessions for the same client.

Maybe we should trigger the wifi close operation using the threshold crossed signal instead of using the health change signal (as it is programmed now), but we have to make sure this signal is sent by the system also when alerts are disabled, which is something I am not 100% sure of and we have to double check.

But definitely we need to make sure to have a way to trigger these kind of operations with a certain degree of tolerance to avoid this annoying flapping which can also add useless burden to the system.