Clean up dead tunnel code

Running go vet on tunnel package returns:
$ go vet ./...
./default.go:929:2: unreachable code
./link.go:104:2: unreachable code
./listener.go:184:2: unreachable code
./session.go:241:2: unreachable code

tunnel/default.go

@@ -919,14 +919,12 @@ func (t *tun) Close() error {
 	default:
 		close(t.closed)
 		t.connected = false
-
-		// send a close message
-		// we don't close the link
-		// just the tunnel
-		return t.close()
 	}
 
-	return nil
+	// send a close message
+	// we don't close the link
+	// just the tunnel
+	return t.close()
 }
 
 // Dial an address