Fix formatting

IPv6 addresses without ports are not enclosed in brackets. They only get
enclosed in brackets in combination with a port.

src/tun2proxy.rs

@@ -30,10 +30,7 @@ pub enum DestinationHost {
 impl std::fmt::Display for DestinationHost {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            DestinationHost::Address(addr) => match addr {
-                IpAddr::V4(_) => addr.fmt(f),
-                IpAddr::V6(_) => write!(f, "[{}]", addr),
-            },
+            DestinationHost::Address(addr) => addr.fmt(f),
             Hostname(name) => name.fmt(f),
         }
     }
@@ -69,7 +66,11 @@ impl From<SocketAddr> for Destination {
 
 impl std::fmt::Display for Destination {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}:{}", self.host, self.port)
+        if let DestinationHost::Address(IpAddr::V6(addr)) = self.host {
+            write!(f, "[{}]:{}", addr, self.port)
+        } else {
+            write!(f, "{}:{}", self.host, self.port)
+        }
     }
 }