fix zrtp bug

diff --git a/oRTP b/oRTP
index 9e186f31a97618cc77d41d5b45ee6eb73873555d..81bc939428560a344999dbe13a30f3ed1b18837d 160000 (submodule)
--- a/oRTP
+++ b/oRTP
@@ -1 +1 @@
-Subproject commit 9e186f31a97618cc77d41d5b45ee6eb73873555d
+Subproject commit 81bc939428560a344999dbe13a30f3ed1b18837d