The next patch includes wire/peer_wire.h and causes a compile error
as lightningd/gossip_control.c defined its own gossip_msg function.
New names are clearer.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Fixes the `short_channel_id` being serialized as 4 bytes block height,
3 bytes transaction index and 1 byte output number, to use 3+3+2 as
the spec says.
The reordering in the unit test structs is mainly to be able to still
use `eq_upto` for tests.