n_tty: Refactor input_available_p() by call site
n_tty: Refactor input_available_p() by call site

Distinguish if caller is n_tty_poll() or n_tty_read(), and
set the read/wakeup threshold accordingly.

Signed-off-by: Peter Hurley <4b8373d016f277527198385ba72fda0feb5da015@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs