Moved the broadcast functionality to broadcast.[ch]. So far this
includes only the enqueuing side of broadcasts, the dequeuing and
actual push to the peer is daemon dependent. This also adds the
broadcast_state to the routing_state and the last broadcast index to
the peer for the legacy daemon.
This is a bit more awkward for large structures, but avoids
indirection for the simpler ones (I copied the structures for the test
code, however). We also remove explicit padding.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>