spender: fix multifundchannel ids.

They're not always 34 (aka '"').  This is a side-effect of ids
changing from u64 to strings quite a while ago.

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

plugins/spender/multifundchannel.c

@@ -14,7 +14,8 @@
 #include <plugins/spender/multifundchannel.h>
 #include <plugins/spender/openchannel.h>
 
-extern const struct chainparams *chainparams;
+/* Global counter to create unique mfc->id values */
+static u64 mfc_id;
 
 /* Which destinations has a value of "all", or -1.  */
 static struct multifundchannel_destination *all_dest(const struct multifundchannel_command *mfc)
@@ -1999,7 +2000,7 @@ json_multifundchannel(struct command *cmd,
 	/* Should exist; it would only nonexist if it were a notification.  */
 	assert(cmd->id);
 
-	mfc->id = *cmd->id;
+	mfc->id = ++mfc_id;
 	mfc->cmd = cmd;
 
 	/* Steal destinations array, and set up mfc pointers */

plugins/spender/multifundchannel.h

@@ -171,9 +171,6 @@ struct multifundchannel_command {
 	multiple `multifundchannel` commands in parallel, or
 	in very close sequence, which might confuse us with
 	*which* debug message belongs with *which* command.
-
-	We actually just reuse the id from the cmd.
-	Store it here for easier access.
 	*/
 	u64 id;