MEDIUM: stream_interfaces: Starts receiving from the upper layers.

MEDIUM: stream_interfaces: Starts receiving from the upper layers.

Instead of waiting for the connection layer to let us know we can read,
attempt to receive as soon as process_stream() is called, and subscribe
to receive events if we can't receive yet.

Now, except for idle connections, the recv(), send() and wake() methods are
no more, all the lower layers do is waking tasklet for anybody waiting
for I/O events.