Handle "throttling" in a single function

Handle "throttling" in a single function

ngIRCd uses "command throttling" and "bps throttling" (bytes per second).
The states are detected in different functions, Conn_Handler() and
Read_Request(), but handle the actual "throttling" in a common function:
this enables us to guarantee consistent behavior and to disable throttling
for special connections in only one place, eventually.