network: load gossip db early

The gossip db is loaded early when the network is started to save
time when the gui is locked and a wallet not yet loaded. Side effects
of the LNWallet to start peering when a channel db is loaded is
circumvented.

electrum/channel_db.py

@@ -613,6 +613,8 @@ class ChannelDB(SqlDB):
     @sql
     @profiler
     def load_data(self):
+        if self.data_loaded.is_set():
+            return
         # Note: this method takes several seconds... mostly due to lnmsg.decode_msg being slow.
         #       I believe lnmsg (and lightning.json) will need a rewrite anyway, so instead of tweaking
         #       load_data() here, that should be done. see #6006