fix(udp/fast-apple): ignore empty cmsghdr #5438

Job	Run time
audit	21s
msrv	16s
features (ubuntu-latest)	2h 2m 49s
lint	1m 21s
features (macos-latest)	36m 45s
test (ubuntu-latest, stable)	1m 1s
features (windows-latest)	1h 10m 8s
test-android (x86_64-linux-android, x86_64, 26)	2m 44s
test (ubuntu-latest, beta)	1m 4s
test-aws-lc-rs	41s
test-android (x86_64-linux-android, x86_64, 25)	2m 23s
test (macos-latest, stable)	58s
test-android (i686-linux-android, x86, 26)	2m 21s
test (windows-latest, stable)	3m 14s
test on freebsd	4m 4s
test-android (i686-linux-android, x86, 25)	2m 28s
test on illumos	7m 24s
test on netbsd	5m 26s
test on solaris	19m 53s
test wasm32-unknown-unknown	55s
	4h 46m 16s

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