mbuf: fix Doxygen comment of distributor metadata

[ upstream commit b3a160230bc0750cc522f456d11aced01d2e9b20 ]

/**< is for post annotations.

Fixes: 839b20b ("ethdev: support metadata as flow rule criteria")

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

lib/mbuf/rte_mbuf_core.h

@@ -686,8 +686,8 @@ struct rte_mbuf {
 				 * @see rte_event_eth_tx_adapter_txq_set()
 				 */
 			} txadapter; /**< Eventdev ethdev Tx adapter */
-			/**< User defined tags. See rte_distributor_process() */
 			uint32_t usr;
+			/**< User defined tags. See rte_distributor_process() */
 		} hash;                   /**< hash information */
 	};