websocket: set $max_payload_size = 128*1024; (131072)

websocket: set $max_payload_size = 128*1024; (131072)

AnyEvent checks rbuf_max after calling the callback (too late), so
we can receive larger data, because AnyEvent uses MAX_READ_SIZE=131072
to fill the buffer.

So a more elegant solution is to set $max_payload_size=128*1024. At least
I am not able to receive rbuf larger than 128*1024 now. But I keep the
protection from the previous patch - just to be sure.