CS:GO A2S_Rules fix does not patch MTU high enough to accommodate all use cases

[Vauff]

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• [x] I have checked that my issue doesn't exist yet.
• [x] I have tried my absolute best to reduce the problem-space and have provided the absolute smallest test-case possible.
• [x] I can always reproduce the issue with the provided description below.

Environment

• Game/AppID (with version if applicable): CS:GO/730

Description

https://github.com/alliedmodders/sourcemod/pull/614 brought the functionality of the A2S_Rules hax plugin directly into SM to fix CS:GO A2S_Rules responses. However while that plugin increased the MTU to 65k bytes, SM's implementation went with a value of 5k instead. This has proven to not be enough for some people that have plugins adding many FCVAR_NOTIFY flagged convars, and causes the A2S_Rules response to fail again after going past 5k bytes.

This should be be a fairly simple PR, but I was unsure of the reasoning for going with a lower value in the first place, and want to make sure there aren't any concerns with 65k or whatever other value may be preferred.

Problematic Code (or Steps to Reproduce)

Enough convars created like this will eventually trigger the issue

ConVar cvar;

public void OnPluginStart()
{
	cvar = CreateConVar("sm_cvar_with_notify_flag", "0", "", FCVAR_NOTIFY);
}

Logs

Some real world examples posted by several users in the SM Discord

[NET] Cannot send 6031-byte packet to ***:7130.  MTU is 1200.  ff ff ff ff 45
[NET] Cannot send 5171-byte packet to 195.201.249.154:47566.  MTU is 1200.  ff ff ff ff 45
[NET] Cannot send 5602-byte packet to [IP]. MTU is 1200. ff ff ff ff 45