codel: fix kernel-doc notation warnings

Use '@' before the struct member names in kernel-doc notation
to prevent kernel-doc warnings.

codel.h:158: warning: Function parameter or member 'ecn_mark' not described in 'codel_stats'
codel.h:158: warning: Function parameter or member 'ce_mark' not described in 'codel_stats'

Fixes: 76e3cc1 ("codel: Controlled Delay AQM")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: Dave Taht <dave.taht@bufferbloat.net>
Link: https://lore.kernel.org/r/20230714045127.18752-4-rdunlap@infradead.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: rddunlap

include/net/codel.h

@@ -145,8 +145,8 @@ struct codel_vars {
  * @maxpacket:	largest packet we've seen so far
  * @drop_count:	temp count of dropped packets in dequeue()
  * @drop_len:	bytes of dropped packets in dequeue()
- * ecn_mark:	number of packets we ECN marked instead of dropping
- * ce_mark:	number of packets CE marked because sojourn time was above ce_threshold
+ * @ecn_mark:	number of packets we ECN marked instead of dropping
+ * @ce_mark:	number of packets CE marked because sojourn time was above ce_threshold
  */
 struct codel_stats {
 	u32		maxpacket;