Fix dtls tests

#[cfg(feature="dtlsv1")]

use connected_socket::Connect;

#[cfg(test)]

#[cfg(feature = "dtlsv1")]

mod udp {

    static mut udp_port:u16 = 15410;

    use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering};

    static UDP_PORT: AtomicUsize = ATOMIC_USIZE_INIT;

    pub fn next_server<'a>() -> String {

        unsafe {

            udp_port += 1;

            format!("127.0.0.1:{}", udp_port)

        }

        let diff = UDP_PORT.fetch_add(1, Ordering::SeqCst);

        format!("127.0.0.1:{}", 15411 + diff)

    }

}