RDMA/cm: Use an attribute_group on the ib_port_attribute intead of kobj's

This code is trying to attach a list of counters grouped into 4 groups to
the ib_port sysfs. Instead of creating a bunch of kobjects simply express
everything naturally as an ib_port_attribute and add a single
attribute_groups list.

Remove all the naked kobject manipulations.

Link: https://lore.kernel.org/r/0d5a7241ee0fe66622de04fcbaafaf6a791d5c7c.1623427137.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>