assert on double-free in debug build

The assert allows easier debugging in gdb by aborting instead of exiting
cleanly. Also a core is generated so a stack trace can be obtained.

Change-Id: I2d05488c4522f4d4570fdfe0283130eb4c853d2a
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/src/vlib/buffer.c b/src/vlib/buffer.c
index 701ddde..77602a6 100644
--- a/src/vlib/buffer.c
+++ b/src/vlib/buffer.c
@@ -339,10 +339,8 @@
 
       if (known != expected_state)
 	{
-	  vlib_panic_with_msg
-	    (vm, "%s %U buffer 0x%x",
-	     is_free ? "freeing" : "allocating",
-	     format_vlib_buffer_known_state, known, bi);
+	  clib_panic ("%s %U buffer 0x%x", is_free ? "freeing" : "allocating",
+		      format_vlib_buffer_known_state, known, bi);
 	}
 
       clib_spinlock_lock (&bm->buffer_known_hash_lockp);