net: core: convert class code to use dev_groups

The dev_attrs field of struct class is going away soon, dev_groups
should be used instead.  This converts the networking core class code to
use the correct field.

In order to do this in the "cleanest" way, some of the macros had to be
changed to reflect the driver core format of naming show/store
functions, which accounts for the majority of the churn in this file.

Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>