rdma: Add stat manual mode support

rdma: Add stat manual mode support

In manual mode a QP can be manually bound to a counter. If the counter
id(cntn) is not specified that kernel will allocate one. After a
successful bind, the cntn can be seen through "rdma statistic qp show".
And in unbind if lqpn is not specified then all QPs on this counter will
be unbound.
The manual and auto mode are mutual-exclusive.

Examples:
$ rdma statistic qp bind link mlx5_2/1 lqpn 178
$ rdma statistic qp bind link mlx5_2/1 lqpn 178 cntn 4
$ rdma statistic qp unbind link mlx5_2/1 cntn 4
$ rdma statistic qp unbind link mlx5_2/1 cntn 4 lqpn 178

Signed-off-by: Mark Zhang <markz@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>