Compat module auto-bounce

[Valery Ushakov]

ttioctl() in sys/tty.c ends with doing

    (void)module_autoload("compat", MODULE_CLASS_ANY);

for ioctls that it doesn't know about.  This causes compat module to
auto-bounce in and out a lot.  Note that this happens even for
up-to-date userland that doesn't need compat code.  E.g. ttyname(3)
uses TIOCPTSNAME which ttioctl() doesn't handle.  Running vi on
console seems to cause compat.mod to be autoloaded twice.

This seems rather wasteful.

-uwe