STC: Don't attempt to use Port access control if it's not supported
STC: Don't attempt to use Port access control if it's not supported

Note that it's still possible for a client to reject the tube if the fallback path is hit, if they
absolutely require Port. This can be done simply by closing the tube.

tiagosh/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt,TelepathyIM/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt4,freedesktop-unofficial-mirror/telepathy__telepathy-qt4,TelepathyIM/telepathy-qt,anantkamath/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt4,special/telepathy-qt-upstream,detrout/telepathy-qt,TelepathyQt/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt,detrout/telepathy-qt,tiagosh/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt,TelepathyIM/telepathy-qt,TelepathyIM/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt4,TelepathyQt/telepathy-qt,detrout/telepathy-qt,tiagosh/telepathy-qt,TelepathyQt/telepathy-qt,special/telepathy-qt-upstream,tiagosh/telepathy-qt,anantkamath/telepathy-qt,anantkamath/telepathy-qt,TelepathyIM/telepathy-qt,TelepathyQt/telepathy-qt,special/telepathy-qt-upstream