FABRIC_MONITOR_TABLE_KEY_SET in APPL_DB when fabric link monitoring feature get disabled

[jfeng-arista]

When fabric link monitoring feature get disabled , the notification in APPL_DB FABRIC_MONITOR_TABLE not get handled properly. If we try to getall of that table, it will get nothing and we can see the key shows FABRIC_MONITOR_TABLE_KEY_SET.
sonic-db-cli -n asic0 APPL_DB keys "F*"