server session CHANGE debug messages for queues

Refs cesnet/netopeer2#465
diff --git a/src/session_server.c b/src/session_server.c
index ee1e5bb..a60f34b 100644
--- a/src/session_server.c
+++ b/src/session_server.c
@@ -881,6 +881,8 @@
 
     /* add ourselves into the queue */
     nc_ps_queue_add_id(ps, id);
+    DBG("PS 0x%p TID %lu queue: added %u, head %u, lenght %u", ps, (long unsigned int)pthread_self(), *id,
+            ps->queue[ps->queue_begin], ps->queue_len);
 
     /* is it our turn? */
     while (ps->queue[ps->queue_begin] != *id) {
@@ -940,6 +942,8 @@
 
     /* remove ourselves from the queue */
     nc_ps_queue_remove_id(ps, id);
+    DBG("PS 0x%p TID %lu queue: removed %u, head %u, lenght %u", ps, (long unsigned int)pthread_self(), id,
+            ps->queue[ps->queue_begin], ps->queue_len);
 
     /* broadcast to all other threads that the queue moved */
     pthread_cond_broadcast(&ps->cond);