Clean up packet queue in udpMuxedConn Close

[codecov[bot]]

Codecov Report

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

Project coverage is 79.17%. Comparing base (ed41bbf) to head (b7d870c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #693 +/- ## ========================================== - Coverage 79.21% 79.17% -0.05% ========================================== Files 41 41 Lines 3733 3735 +2 ========================================== Hits 2957 2957 - Misses 547 548 +1 - Partials 229 230 +1 ``` | [Flag](https://app.codecov.io/gh/pion/ice/pull/693/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pion) | Coverage Δ | | |---|---|---| | [go](https://app.codecov.io/gh/pion/ice/pull/693/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pion) | `79.17% <100.00%> (-0.05%)` | :arrow_down: | | [wasm](https://app.codecov.io/gh/pion/ice/pull/693/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pion) | `22.15% <0.00%> (-0.02%)` | :arrow_down: | 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=pion#carryforward-flags-in-the-pull-request-comment) to find out more.

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