update ms2 with fix for SILK under IOS

diff --git a/mediastreamer2 b/mediastreamer2
index f87ab8a6003c6a9af7ebe9b5818c7e2c04b03a32..887ca16ddda8e5f84d7c64d5decfd7f7c9b92b5d 160000 (submodule)
--- a/mediastreamer2
+++ b/mediastreamer2
@@ -1 +1 @@
-Subproject commit f87ab8a6003c6a9af7ebe9b5818c7e2c04b03a32
+Subproject commit 887ca16ddda8e5f84d7c64d5decfd7f7c9b92b5d