fix stuck poll() when interface down - #987

We were unable to automatically build your code. Please change the build mode for this language to manual and specify build steps for your project. See https://docs.github.com/en/code-security/code-scanning/troubleshooting-code-scanning/automatic-build-failed for more information. Encountered a fatal error while running "/opt/hostedtoolcache/CodeQL/2.25.6/x64/codeql/codeql database trace-command --use-build-mode --working-dir /home/runner/work/netmap/netmap /home/runner/work/_temp/codeql_databases/cpp". Exit code was 2 and error was: A fatal error occurred: Exit status 1 from command: [/opt/hostedtoolcache/CodeQL/2.25.6/x64/codeql/cpp/tools/autobuild.sh]. See the logs for more details.

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