Function nc::swapon

pub fn swapon(filename: &str, flags: i32) -> Result<(), Errno>

Start swapping to file/device.

let filename = "/dev/sda-no-exist";
let ret = nc::swapon(filename, nc::SWAP_FLAG_PREFER);
assert!(ret.is_err());
assert_eq!(ret, Err(nc::EPERM));