update ms2 for syntax error fixes in configure.

diff --git a/mediastreamer2 b/mediastreamer2
index f8ca6065676eff95752d546e387684ccc90e7b1e..5b7873ee3cbc460138015ba244330d99aa861d7f 160000 (submodule)
--- a/mediastreamer2
+++ b/mediastreamer2
@@ -1 +1 @@
-Subproject commit f8ca6065676eff95752d546e387684ccc90e7b1e
+Subproject commit 5b7873ee3cbc460138015ba244330d99aa861d7f