dev: --dev-gossip-time so gossipd doesn't prune old data.

This is useful for canned data, such as the million channels project.

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

lightningd/lightningd.h

@@ -196,6 +196,9 @@ struct lightningd {
 	/* Allow and accept localhost node_announcement addresses */
 	bool dev_allow_localhost;
 
+	/* Timestamp to use for gossipd, iff non-zero */
+	u32 dev_gossip_time;
+
 	/* Things we've marked as not leaking. */
 	const void **notleaks;
 #endif /* DEVELOPER */