MEDIUM: stconn: Properly handle large buffers during a receive

MEDIUM: stconn: Properly handle large buffers during a receive

While large buffers are still unused internally, functions receiving data
from endpoint (connections or applets) were updated to block the receives
when channels are using large buffer and the data forwarding was started.

The goal of this patch is to be able to flush large buffers at the end of
the analyzis stage to return asap on regular buffers.