Tweak maximum MTU for paths using IPv4-mapped IPv6 addresses

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 95.40%. Comparing base (2d26bff) to head (8c3dd7e).

Files	Patch %	Lines
src/connection/path.rs	66.66%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #281 +/- ## =========================================== + Coverage 95.37% 95.40% +0.02% =========================================== Files 50 50 Lines 33474 33482 +8 =========================================== + Hits 31927 31943 +16 + Misses 1547 1539 -8 ```

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