The `route_hop` struct introduced in the previous refactoring is
reused when returning the reply to a `getroute` request. Since these
are nested messages I added the serialization and deserialization
methods.
Some of the struct array helpers need to allocate data when
deserializing their fields. The `getnodes` reply is one such example
that allocates the hostname. Since the change to calling array helpers
the getnodes call was broken because it was attempting to allocate off
of the entry, which did not have a tal header, thus failing.
Christian Decker