Log available liquidity on each channel when starting routefinding

Log available liquidity on each channel when starting routefinding

One of the most common first-steps in troubleshooting routefinding
issues is we ask for the local channel state to determine what the
available HTLC bounds are. While we log first-hop channel details
when we decline to use them, this doesn't tell us if we have
missing channels, and thus here we log all first-hop channels at
the start.

We also take this opportunity to log the limits that were violated
any time we log that we're not using a channel, rather than only
when its a first-hop.