p2p: bump global write timeout to 20s

The previous value of 5 seconds causes timeouts for legitimate messages
if large messages are sent.

p2p/server.go

@@ -30,7 +30,7 @@ const (
 	frameReadTimeout = 30 * time.Second
 
 	// Maximum amount of time allowed for writing a complete message.
-	frameWriteTimeout = 5 * time.Second
+	frameWriteTimeout = 20 * time.Second
 )
 
 var errServerStopped = errors.New("server stopped")