Add libctrl, an SNMP-like control interface

In contrast to the VTY interface the control interface is meant to be
used by programs.
This patch adds basic support, no commands are defined.
diff --git a/openbsc/src/libctrl/Makefile.am b/openbsc/src/libctrl/Makefile.am
new file mode 100644
index 0000000..286929b
--- /dev/null
+++ b/openbsc/src/libctrl/Makefile.am
@@ -0,0 +1,7 @@
+INCLUDES = $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)
+AM_CFLAGS=-Wall $(LIBOSMOCORE_CFLAGS) $(LIBOSMOVTY_CFLAGS) $(COVERAGE_CFLAGS)
+AM_LDFLAGS = $(LIBOSMOCORE_LIBS) $(COVERAGE_LDFLAGS)
+
+noinst_LIBRARIES = libctrl.a
+
+libctrl_a_SOURCES =	control_if.c control_cmd.c