Fix repeated matched event notification

[Barry-Xu-2018]

Address #681

[Barry-Xu-2018]

Although this correction is targeted towards matched events, I guess other events may also have the same issue.

[fujitatomoya]

@MiguelCompany we would like you to review this PR, thanks in advance.

[fujitatomoya]

Just quick heads-up, https://docs.ros.org/en/rolling/Releases/Release-Iron-Irwini.html#release-timeline this must be addressed in this week.

[MiguelCompany]

@Barry-Xu-2018 @fujitatomoya I have taken a deep look into this.

Statuses publication_matched and subscription_matched should be handled specially on the RMW.
In particular, they should always be enabled on the listener mask, since we need track_unique_xxx to be called.

For other statuses, the listener is not called unless an event callback is set for that status.

I have created #683 with what I consider a better approach to fix the repeated notification.

[fujitatomoya]

@MiguelCompany @Barry-Xu-2018

i left a couple of comments, #683. I was not clear that this can address the repeated issue precisely.

[Barry-Xu-2018]

@MiguelCompany thanks for your explanation. I understand.
I close this PR.