fix IOS build

diff --git a/mediastreamer2 b/mediastreamer2
index f77b325c2aa7068adaa5a0c7353b99056732ca48..f87ab8a6003c6a9af7ebe9b5818c7e2c04b03a32 160000 (submodule)
--- a/mediastreamer2
+++ b/mediastreamer2
@@ -1 +1 @@
-Subproject commit f77b325c2aa7068adaa5a0c7353b99056732ca48
+Subproject commit f87ab8a6003c6a9af7ebe9b5818c7e2c04b03a32