Allow Steam IDs in Steam3 format for sm_addban

Exactly what the title says.

sm_addban has some logic to attempt to make sure that the input is a valid Steam Id. (It only supports BANFLAG_AUTHID, not BANFLAG_IP). This makes it support both the Steam3 format now in addition to the legacy Steam2 format.

sm_ban operates on client targetting and already uses the game's network auth string internally. No change is necessary.

sm_unban has a heuristic to detect whether input is an IP address or a Steam Id. This adjusts the heuristic to be more flexible with auth ids, putting the limiting factor on the IP detection.

sm_banip and sm_abortban are (logically) unaffected.