msg: drop the unnecessary polling_stop()

[joscollin]

Drop the unnecessary polling_stop() in the ~RDMAStack(). The RDMADispatcher object contained in
RDMAStack will get distroyed when RDMAStack gets distroyed. Thus ~RDMADispatcher() will be
called automatically and executes the polling_stop().

Fixes:
The below coverity scan reports.

1. CID 1416590:  Memory - corruptions (USE_AFTER_FREE)
    Calling "~RDMADispatcher" frees pointer "this->dispatcher.rx_cq" which has already been freed.
2. CID 1416593:  Memory - illegal accesses (USE_AFTER_FREE)
    Calling "~RDMADispatcher" dereferences freed pointer "this->dispatcher.tx_cc".
3. CID 1416595:  Memory - corruptions (USE_AFTER_FREE)
    Calling "~RDMADispatcher" frees pointer "this->dispatcher.tx_cq" which has already been freed.
4. CID 1416597:  Memory - illegal accesses (USE_AFTER_FREE)
    Calling "~RDMADispatcher" dereferences freed pointer "this->dispatcher.rx_cc".

Signed-off-by: Jos Collin jcollin@redhat.com

[joscollin]

@yuyuyu101
You have created #17080. I think we were working on the same issue in parallel. So please review this PR. Thanks.

[yuriw]

http://pulpito.ceph.com/yuriw-2017-08-21_21:16:27-rados-wip-yuri-testing_2017_8_22-distro-basic-smithi/

http://pulpito.ceph.com/yuriw-2017-08-22_14:54:54-rados-wip-yuri-testing_2017_8_22-distro-basic-smithi/