Update libyang

Our changes which reduced some C++ warnings have been merged upstream.
The CXXFLAGS mangling requires a patch which is now pending a merge.

Change-Id: Ic2b5318eee13ff4f4f3030ac1aaa5ddde67a6c95
Task: https://tree.taiga.io/project/jktjkt-netconf-cli/task/30
diff --git a/submodules/libyang b/submodules/libyang
index c92e2e0..199b42d 160000
--- a/submodules/libyang
+++ b/submodules/libyang
@@ -1 +1 @@
-Subproject commit c92e2e03db17f0f8920997a995f5406da6917cb8
+Subproject commit 199b42d9bdd6ebb16309fc995790ac1c850c2b2e