cleanup in services_dnsmasq_configure, remove duplicate code, for https://github.com/opnsense/core/issues/1182

We only merge chunks for loader.conf leaveraging a priority scheme
in order to be able to override standard modifications made by e.g.
core or plugins (in case of user changes).

Start to work on its scripts, but 20-console is dynamic so it needs
more work in the actual PHP code.

Discussed with: @adschellevis

Reported by: Simon Brunet

PR: https://forum.opnsense.org/index.php?topic=3684

Expand / join the descriptive text and explain floating rules a bit more.

Eventually we should move this kind of "get all attached networks" to a single and simple function, which uses legacy_get_interface_addresses() underneath. but there's still too much obscure code in this region to remove it easily

We don't particularly need this code and the utility as netgraph
is always attached on load as long as we don't detach and the
attach per interface is a custom feature that requires a kernel
patch we don't want to keep around for 17.1.

Only thing we need to measure is the performance impact of not
detaching netgraph.  This only pertains to ethernet devices
anyway.

We do, however, keep interface_netgraph_needed() around for
reference as it's harmless by default.

LDAP fix: handle legal boolean return result from searchUsers()

Carp improvements