Fixes an issue with DropReq where an old client was sending in 14 bytes, but the server was expecting 15 bytes.
To fix this we introduced a new packet handler, `ContainerGridPacketHandler` and changed the code to determine the length of the packet dynamically using `GetLength(NetState)`.
Also fixed throttling so dropped packets are properly skipped.
- [X] Removes 6017 handler since it is only used in one place
- [X] Exposes a ref int to modify the packet length. This is acceptable since we technically have access to the entire reader/buffer.
