Add a mechanism to split unimportant packets if they are greater than the MTU

[IntegratedQuantum]

Related: #819

While this is less important, in the worst case we may end up with a connection just discarding all entity position packet after a certain number of players is exceeded, which would be quite bad.

The easiest/fastest solution would be to construct unimportant protocols such that they can be split into different packets that can be processed independently. This may not always be possible though.