More information in "Unknown beats protocol X"-exception

## Expected Behavior

I have some beats with "Unknown" protocol version that Graylog 2.4.3 does not understand.
I need some more information of the beat sending agent displayed and reduced output in the logs. All this if possible.

## Current Behavior

Current behaviour is like this:
2018-04-26T11:14:42.793+02:00 ERROR [NettyTransport] Error in Input [Beats/5ad61f82a3f2bb438c2d992a] (channel [id: 0x6a2af37f, /remote:port :> /graylognode:port])
java.lang.Exception: Unknown beats protocol version: 3

I have the input behind a load balancer and the address in the error message is showing the load balancers ip.

## Possible Solution

If the information can be found in the received message about who actually is sending this unknown beat protocol it would be nice to have it displayed. It's not that very helpful to know which load balancer is relaying the message.
I hope this is possible to do otherwise I'll have to live with it.

It would also be nice to see if the java stack dump about "unknown beat protocol" could be masked out to only show an error. This to decrease number of rows written to log.

## Steps to Reproduce (for bugs)
no steps given

## Context

## Your Environment
Graylog with different beat versions sending data from clients.
Beats is sent to a load balanced address and relayed to graylog nodes.

* Graylog Version: 2.4.3
* Elasticsearch Version: 5.6.8
* MongoDB Version: 2.6.10
* Operating System: Ubuntu 16.04
* Browser version: not needed