Probe up to second-to-last hop if last was provided by route hint

Probe up to second-to-last hop if last was provided by route hint

If the last hop was provided by route hint we assume it's not an announced channel.
If furthermore only a single route hint is provided we refrain from probing through
all the way to the end and instead probe up to the second-to-last channel.

Optimally we'd do this not based on above mentioned assumption but
rather by checking inclusion in our network graph. However, we don't
have access to our graph in `ChannelManager`.