rdma: Relax requirement to have PID for HW objects

rdma: Relax requirement to have PID for HW objects

RDMA has weak connection between PIDs and HW objects, because
the latter tied to file descriptors for their lifetime management.

The outcome of such connection is that for the following scenario,
the returned PID will be 0 (not-valid):
 1. Create FD and context
 2. Share it with ephemeral child
 3. Create any object and exit that child

This flow was revealed in testing environment and of course real users
are not running such scenario, because it makes no sense at all in RDMA
world.

Let's do two changes in the code to support such workflow anyway:
 1. Remove need to provide PID/kernel name. Code already supports it,
    just need to remove extra validation.
 2. Ball-out in case PID is 0.

Link: https://lore.kernel.org/linux-rdma/20191002123245.18153-2-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: David Ahern <dsahern@kernel.org>