core: io_destroy is missing when destructing reactor, which causes io_context leak
core: io_destroy is missing when destructing reactor, which causes io_context leak

Signed-off-by: Li Fanxi <033b138116f748e2b2c822313607d7a2898371eb@hotmail.com>
Message-Id: <20171009080839.31352-1-033b138116f748e2b2c822313607d7a2898371eb@hotmail.com>

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