BUG/MEDIUM: flt-spoe: Properly handle end of stream from the SPOE applet

BUG/MEDIUM: flt-spoe: Properly handle end of stream from the SPOE applet

The previous fix ("BUG/MEDIUM: applet: Don't pretend to have more data to
handle EOI/EOS/ERROR") revealed an issue with the way the SPOE applet was
reporting the end of stream, leading to never shut the applet down.

In fact, there is two bug in one. The first one is about the applet
shutdown. Since the fix above, the applet is no longer closed. Before, it
was closed because it was reported in error. But now, it is just delayed
because the applet and the SPOP stream are declared to support half close
connections. So the applet is only closed when the SPOP connection is
closed. To fix this bug, both side are now stating that half close
connections are not supported.

The second bug is about the way the end of stream is reported. It is
reported when the ACK response is received. But it is too early, because the
parent stream must process the response first. So now, we take care to have
processed the ACK from the parent applet before reporting an end of stream.

This patch must be backported with the commit above to 3.1.