test: fix flaky flaky udp_mmsg test (#4652) #51

Job	Run time
build-android	4m 0s
build-ios (macos-13)	1m 29s
build-cross-qemu-arm	1m 43s
build-ios (macos-14)	2m 17s
build-cross-qemu-armhf	1m 59s
build-cross-qemu-aarch64	1m 52s
build-linux	1m 42s
build-cross-qemu-riscv64	1m 45s
build-macos (macos-13)	3m 15s
build-cross-qemu-ppc	2m 17s
build-macos (macos-14)	2m 31s
build-cross-qemu-ppc64	1m 44s
build-cross-qemu-ppc64le	1m 57s
build-cross-qemu-s390x	2m 25s
build-cross-qemu-mips	2m 3s
build-cross-qemu-mips64	1m 47s
build-cross-qemu-mipsel	1m 52s
build-cross-qemu-mips64el	2m 1s
build-cross-qemu-arm (u64 slots)	1m 46s
build-cross-qemu-aarch64 (u64 slots)	1m 56s
build-cross-qemu-ppc (u64 slots)	1m 50s
build-cross-qemu-ppc64 (u64 slots)	1m 45s
	45m 56s

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