altq: Clear stats structures in get_class_stats()

These structures are copied out to userspace, and it's possible to leak
uninitialized stack bytes since these routines and their callers weren't
careful to clear them first.  Add memsets to avoid this.

Reported by:	Ilja Van Sprundel <[email protected]>
Reviewed by:	kp, emaste
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D53342

sys/net/altq/altq_cbq.c

@@ -173,6 +173,8 @@ cbq_request(struct ifaltq *ifq, int req, void *arg)
 static void
 get_class_stats(class_stats_t *statsp, struct rm_class *cl)
 {
+	memset(statsp, 0, sizeof(*statsp));
+
 	statsp->xmit_cnt	= cl->stats_.xmit_cnt;
 	statsp->drop_cnt	= cl->stats_.drop_cnt;
 	statsp->over		= cl->stats_.over;

sys/net/altq/altq_fairq.c

@@ -857,6 +857,8 @@ get_class_stats(struct fairq_classstats *sp, struct fairq_class *cl)
 {
 	fairq_bucket_t *b;
 
+	memset(sp, 0, sizeof(*sp));
+
 	sp->class_handle = cl->cl_handle;
 	sp->qlimit = cl->cl_qlimit;
 	sp->xmit_cnt = cl->cl_xmitcnt;

sys/net/altq/altq_priq.c

@@ -597,6 +597,8 @@ priq_purgeq(struct priq_class *cl)
 static void
 get_class_stats(struct priq_classstats *sp, struct priq_class *cl)
 {
+	memset(sp, 0, sizeof(*sp));
+
 	sp->class_handle = cl->cl_handle;
 	sp->qlength = qlen(cl->cl_q);
 	sp->qlimit = qlimit(cl->cl_q);