hardfork: simplify work done on reload

There is no need to fully recalculate and rewrite state, just
refill state from the DB.

src/cryptonote_core/hardfork.h

@@ -189,6 +189,9 @@ namespace cryptonote
     uint8_t get_effective_version(uint8_t version) const;
     bool add(uint8_t block_version, uint64_t height);
 
+    bool rescan_from_block_height(uint64_t height);
+    bool rescan_from_chain_height(uint64_t height);
+
   private:
 
     BlockchainDB &db;