Make quota configurable for DoH
Currently, DoH shares the quota with TCP, which makes
little sense anyway (see tcp-clients option), because of the nature of
interaction of DoH clients: they tend to keep idle opened connections
for longer periods of time, preventing the TCP and TLS client from
being served.
Because of these differences, it makes sense for DoH to have a separate quota facility. Also, it makes sense to make the number of streams per connection configurable as well, as these are treated as virtual connections by the code.
See !5036 (merged) for additional details.