vty: Link osmovty to osmocore as it is using the symbols

Use SUBDIRS to build src first and the src/vty. We will need
to find the right way add the dependencies.
diff --git a/src/Makefile.am b/src/Makefile.am
index 765fbb8..1e97bb9 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1,4 +1,4 @@
-SUBDIRS=vty
+SUBDIRS=. vty
 
 # This is _NOT_ the library release version, it's an API version.
 # Please read Chapter 6 "Library interface versions" of the libtool documentation before making any modification