peer: only add an active link to the channelManager if addPeer succeeds
peer: only add an active link to the channelManager if addPeer succeeds

In this commit we fix an existing bug which could cause internal state
inconsistency between then switch, funding manager, and the peer. Before
this commit, we would _always_ add a new channel to the channelManager.
However, due to recent logic, it may be the case that this isn't the
channel that will ultimately reside in the link. As a result, we would
be unable to process incoming FundingLocked messages properly, as we
would mutate the incorrect channel in memory.

We remedy this by moving the inserting of the new channel into the
activeChannels map until the end of the loadActiveChannels method, where
we know that this will be the link that persists.

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