fix(iroh): `AsyncUdpSocket` backpressure when connection type is not mixed #12215

Job	Run time
Checking docs	53s
Checking fmt	22s
Android Build Only (aarch64-linux-android)	1m 5s
cargo deny	24s
Android Build Only (armv7-linux-androideabi)	1m 3s
check_semver	2m 50s
clippy_check	1m 34s
codespell	6s
Cross Build Only (x86_64-unknown-freebsd)	45s
Cross Test (i686-unknown-linux-gnu)	1m 59s
Minimal Supported Rust Version	1m 8s
Build wasm32	32s
CI Test Suite / Tests (ubuntu-latest, stable, all)	2m 32s
CI Test Suite / Tests (ubuntu-latest, stable, none)	2m 23s
CI Test Suite / Tests (ubuntu-latest, stable, default)	2m 25s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	2m 36s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	2m 25s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	2m 37s
netsim-integration-tests / Netsim	6m 12s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	2m 15s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	2m 8s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	2m 8s
	40m 22s

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