Revert "Increase read buffer size for server connections"

Revert "Increase read buffer size for server connections"

This reverts commit c6e3c13f27744971fcb1d2de4e561d3bcdaa5aed.

This sounded like the right approach at first, but I'm not that sure
that it really makes sense to have different sizes of read buffers: the
per-connection read buffer only needs to keep data that is needed to
parse one full command, be it plain text, encrypted and/or compressed.
Then ngIRCd should handle this one command, move leftover data to the
beginning of the buffer and read the next chunk from the network that is
missing to get the next complete command (512 bytes at max).

So I revert this for now and try to fix the logic in Read_Request(),
which is broken nevertheless, as it results in servers becoming
disconnected during "server burst" when "big" lists are transferred.