app_rpt.c: mutex around link activity macro

[mkmer]

At a minimum, we should be locking the write to the buffer just like every other one.
Without it, we may have flaky behavior executing the macro.

[InterLinked1]

Minor nitpick: "flakey" is misspelled in the commit message

Edit: "Activity" is also misspelled.

I do wonder if the codespell stuff would pick up. GitHub is not very good about ease of reviewing the commit message itself. Gerrit was much better for this. It doesn't seem to now - is there a way to do it with the check?

[mkmer]

https://www.merriam-webster.com/dictionary/flakey
Spell check thinks it's ok because it is....

[InterLinked1]

https://www.merriam-webster.com/dictionary/flakey Spell check thinks it's ok because it is....

But activity wasn't. Is there a way to catch that?
Now that I think about it, even in the Asterisk project, a lot of commit messages have typos. I imagine it's more common for people to hastily throw that together at the end, even if they spend a lot of time on the code.

[mkmer]

Codespell is only running against the source. My browser gives me squiggles in the PR text but nothing is checking the commit messages.