sys/linux: improve iouring interface #14947

Job	Run time
build	13m 38s
dashboard	3m 38s
aux	4m 53s
arch (presubmit_arch_linux)	10m 40s
gvisor	4m 18s
arch (presubmit_arch_freebsd)	6m 31s
old	6m 36s
race	8m 10s
arch (presubmit_arch_netbsd)	4m 23s
arch (presubmit_arch_openbsd)	4m 15s
race_dashboard	4m 12s
arch (presubmit_arch_darwin)	4m 16s
arch (presubmit_arch_windows)	3m 23s
arch (presubmit_arch_executor)	3m 13s
	1h 22m 6s

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