app-layer: improve limits on number of probing parsers

There was an implicit limit of 32 app-layer protocols
used by probing parsers through a mask, meaning that
Suricata should not support more than 32 app-layer protocols
in total.

This limit is relaxed to each flow not being able to
run more than 32 probing parsers, meaning that for each source
and destination port combination, the sum of registered
probing parsers should not exceed 32, even if there are more
than 32 in total.