test: add test for SO_BINDTODEVICE with TCP

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.90%. Comparing base (872b71e) to head (af4a749). Report is 1 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #652 +/- ## ========================================== + Coverage 78.79% 78.90% +0.11% ========================================== Files 21 21 Lines 2546 2546 ========================================== + Hits 2006 2009 +3 + Misses 415 413 -2 + Partials 125 124 -1 ``` | [Flag](https://app.codecov.io/gh/panjf2000/gnet/pull/652/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andy+Pan) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/panjf2000/gnet/pull/652/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andy+Pan) | `78.90% <ø> (+0.11%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andy+Pan#carryforward-flags-in-the-pull-request-comment) to find out more.

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