add silk for IOS

[linphone] / mediastreamer2

diff --git a/mediastreamer2 b/mediastreamer2
index 084ac9a21334d3f91d51666a36bf9f717741f23d..f77b325c2aa7068adaa5a0c7353b99056732ca48 160000 (submodule)
--- a/mediastreamer2
+++ b/mediastreamer2
@@ -1 +1 @@
-Subproject commit 084ac9a21334d3f91d51666a36bf9f717741f23d
+Subproject commit f77b325c2aa7068adaa5a0c7353b99056732ca48