BUG/MEDIUM: stconn: Reset SE descriptor when we fail to create a stream

BUG/MEDIUM: stconn: Reset SE descriptor when we fail to create a stream

If stream_new() fails after the frontend SC is attached, the underlying SE
descriptor is not properly reset. Among other things, SE_FL_ORPHAN flag is
not set again. Because of this error, a BUG_ON() is triggered when the mux
stream on the frontend side is destroyed.

Thus, now, when stream_new() fails, SE_FL_ORPHAN flag is set on the SE
descriptor and its stream-connector is set to NULL.

This patch should solve the issue #1880. It must be backported to 2.6.