In preparation for having the ChannelGraph directly implement the
`routing.Graph` interface, we rename the `ForEachNodeChannel` method to
`ForEachNodeDirectedChannel` since the ChannelGraph already uses the
`ForEachNodeChannel` name and the new name is more appropriate since the
ChannelGraph currently has a `ForEachNodeDirectedChannelTx` method which
passes the same DirectedChannel type to the given call-back.
With this commit we move the traffic shaper definition from the routing
package to the HTLC switch package as a preparation for being able to
use it there as well.
At the same time we rename it to AuxTrafficShaper to be more in line
with the other auxiliary components.
This commit was added to the 0-19-staging branch recently and therefore
didn't make it into a previous part yet. So it's unrelated to the
changes in this part but is required for the whole custom channel saga.
In preparation for structs outside of the `routing` package implementing
this interface, export `routingGraph` and rename it to `Graph` so as to
avoid stuttering.
Pass htlc amount down to the channel so that we don't need to rely
on minHtlc (and pad it when the channel sets a 0 min htlc). Update
test to just check some sane values since we're no longer relying
on minHtlc amount at all.
