BUG/MEDIUM: stconn: Don't needlessly wake the stream on send during fast-forward

BUG/MEDIUM: stconn: Don't needlessly wake the stream on send during fast-forward

With a connection, when data are received, if these data are sent to the
opposite side because the fast-forwarding is possible, the stream may be
woken up on some conditions (at the end of sc_app_chk_snd_conn()):

  * The channel is shut for write
  * The SC is not in the "established" state
  * The stream must explicitly be woken up on write and all data was sent
  * The connection was just established.

A bug on the last condition was introduced with the commit d89884153
("MEDIUM: channel: Use CF_WRITE_EVENT instead of CF_WRITE_PARTIAL"). The
stream is now woken up on any write events.

This patch fixes this issue and restores the original behavior. No backport
is needed.