Previously, when compiling NetworkManager with libaudit support, it
was disabled by default and only used after setting logging.audit=true.
Turn that around. If we compile NetworkManager with audit support, we also
enable it by default. The user can then explicitly disable it by
configuring logging.audit in NetworkManager.conf.
But also, add a configure option 'yes-disabled-by-default' to compile
with audit support, but have it disabled by default. This would be the
previous behavior, but it must be enabled explicitly.
Fixes: be49a59fb6
Introduce some primitives to deliver messages about relevant
configuration changes to the Linux audit subsystem through libaudit
(if enabled at build time) and to the logging system.
