net/sched: netem: add per-impairment extended statistics

Add 64-bit counters for each impairment netem applies (delay, loss,
ECN marking, corruption, duplication, reordering) and for skb
allocation failures during enqueue. Exposed through TCA_STATS_APP
as struct tc_netem_xstats.

Counters increment when an impairment is occurs, independent of later
events that may mask its on-wire effect. Added allocation_errors
(similar to sch_fq) to account for when impairment could not be
applied due to memory pressure, etc.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Link: https://patch.msgid.link/20260509171123.307549-6-stephen@networkplumber.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/uapi/linux/pkt_sched.h

@@ -569,6 +569,16 @@ struct tc_netem_gemodel {
 #define NETEM_DIST_SCALE	8192
 #define NETEM_DIST_MAX		16384
 
+struct tc_netem_xstats {
+	__u64	delayed;	/* packets delayed */
+	__u64	dropped;	/* packets dropped by loss model      */
+	__u64	corrupted;	/* packets with bit errors injected   */
+	__u64	duplicated;	/* duplicate packets generated        */
+	__u64	reordered;	/* packets sent out of order          */
+	__u64	ecn_marked;	/* packets ECN CE-marked (not dropped)*/
+	__u64	allocation_errors;
+};
+
 /* DRR */
 
 enum {