bonding: introduce and use port_params structure

It generally helps to handle those values in various places, using it
might make the code more readable and gives room for other improvements.

The IEEE standard talks about them as "parameter values".

Signed-off-by: Holger Eitzenberger <holger@eitzenberger.org>
Signed-off-by: David S. Miller <davem@davemloft.net>