main: allow daemonizing again - initialize become_daemon to TRUE (bgo #701383)

7ff3d1500e reversed become_daemon for
"--no-daemon" with G_OPTION_FLAG_REVERSE, but missed to reverse initialization
into become_daemon=TRUE and thus NM couldn't be daemonized.

https://bugzilla.gnome.org/show_bug.cgi?id=701383

src/main.c

@@ -303,7 +303,7 @@ int
 main (int argc, char *argv[])
 {
 	GOptionContext *opt_ctx = NULL;
-	gboolean become_daemon = FALSE, run_from_build_dir = FALSE;
+	gboolean become_daemon = TRUE, run_from_build_dir = FALSE;
 	gboolean debug = FALSE;
 	gboolean g_fatal_warnings = FALSE;
 	gs_free char *pidfile = NULL;