sys/linux: improve iouring interface #14948

Job	Run time
build	14m 20s
dashboard	3m 31s
aux	4m 46s
arch (presubmit_arch_linux)	10m 48s
arch (presubmit_arch_freebsd)	6m 33s
gvisor	4m 11s
old	6m 33s
arch (presubmit_arch_netbsd)	4m 24s
race	8m 15s
arch (presubmit_arch_openbsd)	4m 20s
race_dashboard	4m 12s
arch (presubmit_arch_darwin)	4m 19s
arch (presubmit_arch_windows)	3m 26s
arch (presubmit_arch_executor)	3m 14s
	1h 22m 52s

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