Take into account RTP packets header sizes when calculating BWE and pacing #1996

Job	Run time
lint	38s
cargo-deny (aarch64-apple-ios)	22s
test (ubuntu-latest, stable)	1m 47s
test (ubuntu-latest, beta)	1m 47s
cargo-deny (aarch64-linux-android)	21s
test (ubuntu-latest, 1.65.0)	2m 25s
cargo-deny (i686-pc-windows-gnu)	21s
cargo-deny (i686-pc-windows-msvc)	22s
test (macos-latest, stable)	1m 45s
cargo-deny (i686-unknown-linux-gnu)	21s
test (macos-latest, beta)	1m 12s
cargo-deny (wasm32-unknown-unknown)	18s
test (macos-latest, 1.65.0)	1m 23s
cargo-deny (x86_64-apple-darwin)	19s
test (windows-latest, stable)	3m 44s
cargo-deny (x86_64-apple-ios)	21s
test (windows-latest, beta)	2m 49s
cargo-deny (x86_64-pc-windows-gnu)	20s
test (windows-latest, 1.65.0)	3m 39s
cargo-deny (x86_64-pc-windows-msvc)	21s
cargo-deny (x86_64-unknown-linux-gnu)	22s
cargo-deny (x86_64-unknown-redox)	19s
	25m 16s

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