Improve FPM check

[tinect]

Not sure this will work like you expect:

2. max-children-reached is a counter, that means it can be 12, but that last increase by 1 is many days ago.

3. max-listen-queue is the same.

Originally posted by @beberlei in #336 (comment)

[tinect]

In my opinion, this isn't an issue; altering the setting requires a server restart, thus resetting the counter.

But we could check if we could improve it.