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: 76e3cc126bb2 ("codel: Controlled Delay AQM")
Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Jamal Hadi Salim <[e-mail]>
Cc: Cong Wang <[e-mail]>
Cc: Jiri Pirko <[e-mail]>
Cc: Dave Taht <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/codel.h

···
  * @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;