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 openzfs#13648
Closes openzfs#13685

tests/zfs-tests/tests/functional/io/io_uring.ksh

@@ -40,7 +40,7 @@
 verify_runnable "global"
 
 
-if [[ $(linux_version) -lt $(linux_version "5.1") ]]; then
+if ! $(grep -q "CONFIG_IO_URING=y" /boot/config-$(uname -r)); then
 	log_unsupported "Requires io_uring support"
 fi