lightningd: disable topology timers on shutdown.

Not necessary yet, but it will be once shutdown starts waiting for
plugins to respond: we don't want these to try to access the bcli
plugin once it's freed.

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

lightningd/bitcoind.h

@@ -32,6 +32,9 @@ struct bitcoind {
 	/* Ignore results, we're shutting down. */
 	bool shutdown;
 
+	/* Timer if we're waiting for it to warm up. */
+	struct oneshot *checkchain_timer;
+
 	struct list_head pending_getfilteredblock;
 
 	/* Map each method to a plugin, so we can have multiple plugins