implement notifications when doing transfers

[linphone] / mediastreamer2

diff --git a/mediastreamer2 b/mediastreamer2
index 9d722a1456c8574b385fac0eadf4ad6a4067637b..1b517a0bc1d6559267143130d137d0252a05f752 160000 (submodule)
--- a/mediastreamer2
+++ b/mediastreamer2
@@ -1 +1 @@
-Subproject commit 9d722a1456c8574b385fac0eadf4ad6a4067637b
+Subproject commit 1b517a0bc1d6559267143130d137d0252a05f752