channeldb: update chanid in-mem during MarkAsOpen
channeldb: update chanid in-mem during MarkAsOpen

Modifies the MarkAsOpen operation to also update the
ShortChanID and IsPending fields in-memory. Before,
only the on-disk representation was updated, which
may have lead to stale data channel states being
passed in-memory.

LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd