OutgoingStreamTubeChannel: Make the parameters arg to the offer fns optional
OutgoingStreamTubeChannel: Make the parameters arg to the offer fns optional

Most tube apps don't seem to use the parameters at all, so it doesn't seem useful to require passing
them.

To be clear: this is both API and ABI backwards compatible, as C++ optional arguments are a compile
time feature and we're just adding possibilities here.

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