htlcswitch/link: add ChannelPoint() to retrieve the channel outpoint.

This function will be used in the switch to retrieve the channel point for a link,
allowing the switch to retrieve individual channels from the database.

htlcswitch/mock.go

@@ -673,6 +673,7 @@ func (f *mockChannelLink) ChanID() lnwire.ChannelID                     { return
 func (f *mockChannelLink) ShortChanID() lnwire.ShortChannelID           { return f.shortChanID }
 func (f *mockChannelLink) Bandwidth() lnwire.MilliSatoshi               { return 99999999 }
 func (f *mockChannelLink) Peer() lnpeer.Peer                            { return f.peer }
+func (f *mockChannelLink) ChannelPoint() *wire.OutPoint                 { return &wire.OutPoint{} }
 func (f *mockChannelLink) Stop()                                        {}
 func (f *mockChannelLink) EligibleToForward() bool                      { return f.eligible }
 func (f *mockChannelLink) setLiveShortChanID(sid lnwire.ShortChannelID) { f.shortChanID = sid }