Function netsim::spawn::behind_nat_v4

pub fn behind_nat_v4<F, R>(
    handle: &Handle, 
    nat: NatV4Builder, 
    public_ip: Ipv4Addr, 
    func: F
) -> (JoinHandle<R>, Ipv4Plug) where
    R: Send + 'static,
    F: FnOnce() -> R + Send + 'static, 

Spawn a thread with a single interface, operating a behind a NAT.