[IrDA]: LMP discovery timer not started by default

By default, LMP sets up a 3 seconds timer for discovery.
We don't need it until discovery is set to 1.

Signed-off-by: Ross Burton <ross@openedhand.com>
Signed-off-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>