transports/noise: Have NoiseAuthenticated::xx use X25519Spec

We support two versions of the Noise XX handshake with X25519, but only one of
them is compliant with the specification and thus compliant with other
implementations. We should always default to the spec compliant handshake.

Fixes bug introduced in libp2p#2887

transports/noise/src/lib.rs

@@ -390,12 +390,12 @@ pub struct NoiseAuthenticated<P, C: Zeroize, R> {
     config: NoiseConfig<P, C, R>,
 }
 
-impl NoiseAuthenticated<XX, X25519, ()> {
+impl NoiseAuthenticated<XX, X25519Spec, ()> {
     /// Create a new [`NoiseAuthenticated`] for the `XX` handshake pattern using X25519 DH keys.
     ///
     /// For now, this is the only combination that is guaranteed to be compatible with other libp2p implementations.
     pub fn xx(id_keys: &identity::Keypair) -> Result<Self, NoiseError> {
-        let dh_keys = Keypair::<X25519>::new();
+        let dh_keys = Keypair::<X25519Spec>::new();
         let noise_keys = dh_keys.into_authentic(id_keys)?;
         let config = NoiseConfig::xx(noise_keys);