chaintopology: restore anchor timeout.

Instead of using wall-clock time, we use blocks.  This is simpler and
better for database restores.  And both sides will time out.

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

daemon/lightningd.h

@@ -20,6 +20,9 @@ struct config {
 	/* How long do we let them lock up our funds? (blocks) */
 	u32 locktime_max;
 
+	/* How many blocks before we expect to see anchor?. */
+	u32 anchor_onchain_wait;
+
 	/* How many confirms until we consider an anchor "settled". */
 	u32 anchor_confirms;