[202205] Preserve copp tables through DB migration (#2524) (#2574)

- What I did
Preserve COPP table contents through DB migration. (Mellanox only)

- How I did it
Skipped deleting of COPP tables in DB migrator

- How to verify it
Observe COPP table contents are preserved right after reboot

scripts/db_migrator.py

@@ -844,7 +844,8 @@ def common_migration_ops(self):
                 new_cfg = {**init_cfg, **curr_cfg}
                 self.configDB.set_entry(init_cfg_table, key, new_cfg)
 
-        self.migrate_copp_table()
+        if self.asic_type != "mellanox":
+            self.migrate_copp_table()
         if self.asic_type == "broadcom" and 'Force10-S6100' in self.hwsku:            
             self.migrate_mgmt_ports_on_s6100()
         else: