This stores and reads the channel_announcements in the wrapping message which
allows us to store associated data with the raw channel_announcements.
The gossip_store applies channel_announcements directly but it also returns it,
and it gets discarded as a duplicate. In the next commit we'll have gossip_store
apply all changes, bypassing verification, so the duplication is only temporary.
Signed-off-by: Christian Decker <decker.christian@gmail.com>
Christian Decker