fix: Try improving `relay_datagram_send_channel()` #12179

Job	Run time
Cross Build Only (x86_64-unknown-freebsd)	44s
Android Build Only (aarch64-linux-android)	1m 4s
Checking docs	1m 4s
Android Build Only (armv7-linux-androideabi)	1m 6s
Checking fmt	27s
check_semver	4m 6s
Cross Test (i686-unknown-linux-gnu)	1m 58s
Build wasm32	33s
cargo deny	27s
clippy_check	2m 10s
codespell	7s
Minimal Supported Rust Version	1m 3s
netsim-integration-tests / Netsim	5m 43s
CI Test Suite / Tests (ubuntu-latest, stable, all)	2m 50s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	2m 29s
CI Test Suite / Tests (ubuntu-latest, stable, none)	2m 22s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	2m 6s
CI Test Suite / Tests (ubuntu-latest, stable, default)	2m 41s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	2m 8s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	3m 2s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	2m 18s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	2m 38s
	43m 6s

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