lib/util: convert DBG_STARTUP_NOTICE() to use debug_set_forced_log_priority(DBGLVL_NO...

lib/util: convert DBG_STARTUP_NOTICE() to use debug_set_forced_log_priority(DBGLVL_NOTICE)

Using -1 as log level is not compatible without our infrastructure.

As all backends are initialized with .log_level = -1, which means
they don't log the message, but now they all try to handle the
startup message even if they are not configured.

E.g. is means that systemd's journalctl get the message twice
now, first via the syslog and also the systemd backend.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15377

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Björn Jacke <bjacke@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>