lightningd: trace JSON id prefixes through sendrawtx.

First, merge the _ahf_ and non-ahf interfaces.
Second, remove the always-NULL txs->cmd field.

Then, add optional id_prefix for bitcoind_sendrawx, so if it's
triggered by a command (e.g. "withdraw") it's shown correctly in logs.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/dual_open_control.c

@@ -1561,7 +1561,13 @@ static void send_funding_tx(struct channel *channel,
 		  type_to_string(tmpctx, struct wally_tx, cs->wtx));
 
 	bitcoind_sendrawtx(ld->topology->bitcoind,
+			   channel->open_attempt
+			   ? (channel->open_attempt->cmd
+			      ? channel->open_attempt->cmd->id
+			      : NULL)
+			   : NULL,
 			   tal_hex(tmpctx, linearize_wtx(tmpctx, cs->wtx)),
+			   false,
 			   sendfunding_done, cs);
 }