ZTS: Fix io_uring support check

Not all Linux distribution kernels enable io_uring support by
default. Update the run time check to verify that the booted
kernel was built with CONFIG_IO_URING=y.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Co-authored-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #13648
Closes #13685