IB/mlx5: Expose RoCE accelerator counters

Introduce the following RoCE accelerator counters:
* roce_adp_retrans - number of adaptive retransmission for RoCE traffic.
* roce_adp_retrans_to - number of times RoCE traffic reached time out
  due to adaptive retransmission.
* roce_slow_restart - number of times RoCE slow restart was used.
* roce_slow_restart_cnps - number of times RoCE slow restart
  generate CNP packets.
* roce_slow_restart_trans - number of times RoCE slow restart change
  state to slow restart.

Link: https://lore.kernel.org/r/20200115145459.83280-3-leon@kernel.org


Signed-off-by: Avihai Horon <avihaih@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>