Improve fetch limit logging

Improve fetch limit logging

When initially hitting the `fetches-per-zone` value, a log message
is being generated for the event of dropping the first fetch, then
any further log events occur only when another fetch is being dropped
and 60 seconds have been passed since the last logged message.

That logic isn't ideal because when the counter of the outstanding
fetches reaches zero, the structure holding the counters' values will
get deleted, and the information about the dropped fetches accumulated
during the last minute will not be logged.

Improve the fcount_logspill() function to makie sure that the final
values are getting logged before the counter object gets destroyed.