RDMA/counter: Combine allocation and bind logic

RDMA counters are allocated and bounded to QP immediately after that.
Only after this two step process they are really usable. By combining
the logic, we are ensuring that once counter is returned to the caller,
it will have everything set.

Link: https://lore.kernel.org/r/20201104144008.3808124-3-leon@kernel.org


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