RDMA/nldev: Allow get default counter statistics through RDMA netlink

This patch adds the ability to return the hwstats of per-port default
counters (which can also be queried through sysfs nodes).

Signed-off-by: Mark Zhang <markz@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>