net/i40e: downgrade unnecessary error log

When receiving the unsupported AQ messages, it's taken as
an error. It's not appropriate and triggers too much
unnecessary print.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>

drivers/net/i40e/i40e_ethdev.c

@@ -5782,7 +5782,7 @@ i40e_dev_handle_aq_msg(struct rte_eth_dev *dev)
 					RTE_ETH_EVENT_INTR_LSC, NULL);
 			break;
 		default:
-			PMD_DRV_LOG(ERR, "Request %u is not supported yet",
+			PMD_DRV_LOG(DEBUG, "Request %u is not supported yet",
 				    opcode);
 			break;
 		}