Improve tcpdump legibility.

src/include/gpxe/aoe.h

 #define AOE_CMD_ATA	0x00	/**< Issue ATA command */
 #define AOE_CMD_CONFIG	0x01	/**< Query Config Information */
 
+#define AOE_TAG_MAGIC	0xebeb0000
+
 #define AOE_ERR_BAD_COMMAND	1 /**< Unrecognised command code */
 #define AOE_ERR_BAD_PARAMETER	2 /**< Bad argument parameter */
 #define AOE_ERR_UNAVAILABLE	3 /**< Device unavailable */

src/net/aoe.c

  */
 void aoe_open ( struct aoe_session *aoe ) {
 	memset ( aoe->target, 0xff, sizeof ( aoe->target ) );
+	aoe->tag = AOE_TAG_MAGIC;
 	aoe->timer.expired = aoe_timer_expired;
 	list_add ( &aoe->list, &aoe_sessions );
 }