protect against unregistering NULL observer

Signed-off-by: Eyal Salomon <esalomon@mellanox.com>
reducing amount of tasks
in userspace, using continuous pages to register the tasks's buffers

Signed-off-by: Eyal Salomon <esalomon@mellanox.com>
removing unused parameter

Signed-off-by: Eyal Salomon <esalomon@mellanox.com>