unix,win: error on zero delay tcp keepalive #1

Job	Run time
build-android	2m 8s
build-ios	1m 54s
build-cross-qemu-arm	1m 33s
build-linux	1m 57s
build-macos	3m 55s
build-cross-qemu-armhf	1m 34s
build-cross-qemu-aarch64	1m 55s
build-cross-qemu-riscv64	1m 30s
build-cross-qemu-ppc	1m 37s
build-cross-qemu-ppc64	1m 37s
build-cross-qemu-ppc64le	1m 33s
build-cross-qemu-s390x	1m 30s
build-cross-qemu-mips	1m 34s
build-cross-qemu-mips64	1m 38s
build-cross-qemu-mipsel	1m 34s
build-cross-qemu-mips64el	1m 36s
build-cross-qemu-arm (u64 slots)	1m 38s
build-cross-qemu-aarch64 (u64 slots)	1m 43s
build-cross-qemu-ppc (u64 slots)	1m 33s
build-cross-qemu-ppc64 (u64 slots)	2m 0s
	35m 59s

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