daemon: Disable logging to console after detaching.

When we detach, we replace stderr by /dev/null, so there's no point in
logging to the console after that.  Just turn it off.

lib/daemon.c

@@ -408,6 +408,9 @@ close_standard_fds(void)
         dup2(null_fd, STDOUT_FILENO);
         dup2(null_fd, STDERR_FILENO);
     }
+
+    /* Disable logging to stderr to avoid wasting CPU time. */
+    vlog_set_levels(NULL, VLF_CONSOLE, VLL_EMER);
 }
 
 /* If daemonization is configured, then starts daemonization, by forking and