gossipd: invalidate old gossip_stores.

Incrementing version number means stores which were prior to the previous
commit will be removed, and refreshed.  The simplest fix, if not the most
efficient.

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

gossipd/gossip_store.h

@@ -11,7 +11,7 @@
 /**
  * gossip_store -- On-disk storage related information
  */
-#define GOSSIP_STORE_VERSION 2
+#define GOSSIP_STORE_VERSION 3
 
 struct gossip_store;
 struct routing_state;

tests/test_gossip.py

@@ -822,7 +822,7 @@ def test_gossip_store_load(node_factory):
     """Make sure we can read canned gossip store"""
     l1 = node_factory.get_node(start=False)
     with open(os.path.join(l1.daemon.lightning_dir, 'gossip_store'), 'wb') as f:
-        f.write(bytearray.fromhex("02"  # GOSSIP_VERSION
+        f.write(bytearray.fromhex("03"  # GOSSIP_VERSION
                                   "00000099"  # len
                                   "12abbbba"  # csum
                                   "1002"  # WIRE_GOSSIP_STORE_NODE_ANNOUNCEMENT