yaml: add and comment missing dns settings

DNS memcap settings "global-memcap" and "state-memcap" were missing.

Additionally, add request-flood setting.
dns: fix message of decoder rule 2240008

The message now reflects that the rule matches on:
    app-layer-event:dns.state_memcap_reached;
app-layer-event: make error reporting more clear

If the protocol is disabled, app-layer-event would print a cryptic
error message. This patch makes sure we inform the user the protocol
is in fact disabled.
dns yaml: fix detect ports of tcp relying on udp

The probing parser detection ports yaml settings of the TCP part
of the DNS parser accidentally used udp as protocol string, causing
the wrong part of the YAML to be evaluated.
app-layer: tell pp registrar if config was found

The probing parser registration function
AppLayerProtoDetectPPParseConfPorts was a void, meaning it would
give no feedback to the registering protocol implementation. If a
config was missing, it would just give up.

This patch changes it to return a bool. 0 if no config was found,
1 if a config was found.

This allows the caller to setup a default case.
dns: if no (valid) config is found, use defaults

This patch will set up probing parsers if no (valid) config is
found.

Add a warning in those cases.