private-tubes-factory.c: add generic tubes caps
private-tubes-factory.c: add generic tubes caps

Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,mlundblad/telepathy-gabble