his patch moves the internal storage of the offset and period to the
transport class and adds methods to set them (there's no need for a get
method since the value in the transport class is exactly what the driver
believes the transport agreement to be).

You can see how this type of use of the transport class is supposed to
work: the driver now has init and exit routines attaching and releasing
the transport class (that's the reason for the Makefile perturbation
because it has to init before its users).  The correct attributes are
set up in slave_configure() for negotiation and we now export the period
and offset setting functions.