irnet: ppp: move IRNET_MINOR to include/linux/miscdevice.h

This patch move the define for IRNET_MINOR to include/linux/miscdevice.h
It is better that all minor number definitions are in the same place.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>