Retain fgnhg state db table entry during warm reboot (sonic-net#1315)

Add FG_ROUTE_TABLE to backup database for warm reboot support for fgnhg.

scripts/fast-reboot

@@ -233,11 +233,13 @@ function backup_database()
     debug "Backing up database ..."
     # Dump redis content to a file 'dump.rdb' in warmboot directory
     mkdir -p $WARM_DIR
-    # Delete keys in stateDB except FDB_TABLE|*, MIRROR_SESSION_TABLE|*, WARM_RESTART_ENABLE_TABLE|*
+
+    # Delete keys in stateDB except FDB_TABLE|*, MIRROR_SESSION_TABLE|*, WARM_RESTART_ENABLE_TABLE|*, FG_ROUTE_TABLE|*
     redis-cli -n 6 eval "
         for _, k in ipairs(redis.call('keys', '*')) do
             if not string.match(k, 'FDB_TABLE|') and not string.match(k, 'WARM_RESTART_TABLE|') \
                                           and not string.match(k, 'MIRROR_SESSION_TABLE|') \
+                                          and not string.match(k, 'FG_ROUTE_TABLE|') \
                                           and not string.match(k, 'WARM_RESTART_ENABLE_TABLE|') then
                 redis.call('del', k)
             end