lib: apply minor dtls cleanups #7534

Job	Run time
Build slim tarball	1m 11s
aarch64-linux: Cache V8 build	23s
aarch64-darwin: with shared libraries	26m 52s
x86_64-linux: with shared libraries	30m 34s
x86_64-darwin: with shared libraries	35m 13s
aarch64-linux: with shared openssl-1.1.1w	25m 29s
aarch64-linux: with shared openssl-3.5.6	25m 57s
aarch64-linux: with shared openssl-4.0.0	24m 53s
aarch64-linux: with shared openssl-3.6.2	26m 9s
aarch64-linux: with shared boringssl-0.20260508.0	25m 25s
aarch64-linux: with shared openssl-3.0.20	25m 1s
	4h 7m 7s

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