The spec 4af8e1841151f0c6e8151979d6c89d11839b2f65 uses a 32-byte 'channel-id'
field, not to be confused with the 8-byte short ID used by gossip. Rename
appropriately, and update to the new handshake protocol.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>