buffers: protect against bad thread indices
There is a very rare bug in NAT processing that yeilds a thread
index of ~0.  When this happens, vlib_get_frame_queue_elt()
suffers a segfault and VPP quits.  Prevent an outright fault
by dropping the packet instead.
Type: fix
@@ -261,6 +261,9 @@ vlib_get_frame_queue_elt (vlib_frame_queue_main_t *fqm, u32 index,
vlib_frame_queue_t *fq;
u64 nelts, tail, new_tail;
+ if (index >= vec_len (fqm->vlib_frame_queues))
+ return 0;
+
fq = fqm->vlib_frame_queues[index];
ASSERT (fq);
nelts = fq->nelts;
