Android API level <= 25 fails sendmsg ECN with InvalidInput

[mxinden]

When running the quinn-udp ecn_* unit tests sendmsg fails with:

2024-08-22T14:41:30.636494Z  WARN quinn_udp: sendmsg error: Os { code: 22, kind: InvalidInput, message: "Invalid argument" }, Transmit: { destination: 127.0.0.1:50196, src_ip: None, enc: Some(Ect0), len: 5, segment_size: None }

https://github.com/quinn-rs/quinn/blob/cef42cccef6fb6f02527ae4b2f42d7f7da878f62/quinn-udp/tests/tests.rs#L34-L153

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I don't have a fix (yet). Opening this early to publish the reproducer. See failing CI.

Any ideas anyone?

Depends on https://github.com/quinn-rs/quinn/pull/1973.