Exclude NUL characters from OSStrings returned by getsockopt #1654

Job	Run time
macos	2m 51s
linux_native_builds (x86_64-unknown-linux-gnu)	27s
linux_native_builds (x86_64-unknown-linux-musl)	29s
macos-aarch64	1m 35s
minver	15s
rust_stable	1m 20s
rustfmt	5s
solaris (x86_64-pc-solaris)	3m 23s
tier3 (x86_64-unknown-dragonfly)	1m 0s
tier3 (x86_64-unknown-openbsd)	1m 2s
tier3 (x86_64-unknown-haiku)	57s
tier3 (armv7-unknown-linux-uclibceabihf)	1m 13s
cross_compiling	0s
redox	0s
cross	0s
	14m 37s

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