rdma: Add optional-counter option to rdma stat bind commands

rdma: Add optional-counter option to rdma stat bind commands

Add a new optional filter named optional-counter to commands:
rdma stat qp set link [link_name] auto

The new filter value can be either on or off and it must be the last
provided filter in the command, not providing it would be the same as off.

It indicates that when binding counters to a QP we also want the
currently enabled optional-counters on the link to be bound as well.

In addition Adjust rdma statistic man page to reflect the new
optional-counter changes.

Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>