Stop when all listening sockets have closed

[qris]

Otherwise, if select() is blocking, with a control socket (close_pipe) remaining in sniff_sockets, the loop will never terminate.

Checklist:

• [X] If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• [X] I squashed commits belonging together
• [ ] I added unit tests or explained why they are not relevant
• [ ] I executed the regression tests for Python2 and Python3 (using tox or, cd test && ./run_tests_py2, cd test && ./run_tests_py3)
• [ ] If the PR is still not finished, please create a Draft Pull Request

If select() is blocking, with a control socket (close_pipe) remaining in sniff_sockets, the loop will never terminate. This change fixes that.

fixes #xxx

[gpotter2]

Thanks for the report. Good point although the proposed fix is rather inefficient. It would be best to compute this list (set?) only once

[stryngs]

@qris Are you still pursuing this?

[qris]

No, sorry, I'm not using Scapy at the moment.

[gpotter2]

This was fixed in https://github.com/secdev/scapy/pull/3663.