Remove the distinction between user CB and kernel CB, and verify for
both that they are not destroyed more than once.

As kernel CB might be taken from the pre-allocated CB pool, so we need
to clear the handle destroyed indication when returning a CB to the
pool.
Signed-off-by: Tomer Tayar <ttayar@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>