terminal-util: change 2nd parameter of terminal_reset_defensive() to flags

let's convert the 2nd argumeng form a boolean to a proper flags
parameter. Doesn't change behaviour in anyway, but is more readable, and
prepares ground for adding more flags soon.

src/firstboot/firstboot.c

@@ -121,7 +121,7 @@ static void print_welcome(int rfd) {
         pn = os_release_pretty_name(pretty_name, os_name);
         ac = isempty(ansi_color) ? "0" : ansi_color;
 
-        (void) terminal_reset_defensive_locked(STDOUT_FILENO, /* switch_to_text= */ false);
+        (void) terminal_reset_defensive_locked(STDOUT_FILENO, /* flags= */ 0);
 
         if (colors_enabled())
                 printf("\nWelcome to your new installation of \x1B[%sm%s\x1B[0m!\n", ac, pn);