We alternated between using a sha256 and using a privkey, but there are
numerous places where we have a random 32 bytes which are neither.
This fixes many of them (plus, struct privkey is now defined in terms of
struct secret).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Raw crypto_state is what we send across the wire: the peer one is for
use in async crypto io routines (peer_read_message/peer_write_message).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
