Reason: In acceptor_poller_unregistered_event, we
directly call spdk_nvmf_check_pools and spdk_app_stop,
it will fail the memory check.
And function nvmf_delete_subsystem_poller_unreg will
not be called since we already call spdk_app_stop.
Change-Id: I3ffa30c87b149a66cee1d87d1bb81d4dc8cc96b9
Signed-off-by: Ziye Yang <ziye.yang@intel.com>