add support in the api for multi transport

[linphone] / mediastreamer2

diff --git a/mediastreamer2 b/mediastreamer2
index 2c65063096918cce1dfcc6f01c0cbf43c3232dc0..a6484a8463b62a60d03ef8358b2e305408f3b011 160000 (submodule)
--- a/mediastreamer2
+++ b/mediastreamer2
@@ -1 +1 @@
-Subproject commit 2c65063096918cce1dfcc6f01c0cbf43c3232dc0
+Subproject commit a6484a8463b62a60d03ef8358b2e305408f3b011