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/vty/Makefile.am b/src/vty/Makefile.am
index f2859cf..7353ab8 100644
--- a/src/vty/Makefile.am
+++ b/src/vty/Makefile.am
@@ -10,4 +10,5 @@
 
 libosmovty_la_SOURCES = buffer.c command.c vty.c vector.c utils.c \
 			telnet_interface.c logging_vty.c
+libosmovty_la_LIBADD = $(top_builddir)/src/libosmocore.la
 endif