add sdp_msg API: SDP parsing/composition

Rationale: in order to add full SDP to the MNCC protocol (upcoming patch
I8c3b2de53ffae4ec3a66b9dabf308c290a2c999f), we need to parse and compose SDP
messages. Obviously, libosmo-mgcp-client already contains similar code, but
that is unfortunately heavily glued to the actual MGCP implementation. The
simplest solution is to create this separate implementation, copy-pasting from
the existing libosmo-mgcp-client code as is convenient.

This API is added here to probe whether it works well. When it does, the
intention is to "move it up" to osmo-mgw and overhaul the SDP parsing in our
MGCP client and MGCP server APIs using this same API.

Change-Id: If3ce23cd5bab15e2ab4c52ef3e4c75979dffe931
diff --git a/tests/sdp_msg/Makefile.am b/tests/sdp_msg/Makefile.am
new file mode 100644
index 0000000..7d8def9
--- /dev/null
+++ b/tests/sdp_msg/Makefile.am
@@ -0,0 +1,32 @@
+AM_CPPFLAGS = \
+	$(all_includes) \
+	-I$(top_srcdir)/include \
+	$(NULL)
+
+AM_CFLAGS = \
+	-Wall \
+	-ggdb3 \
+	$(LIBOSMOCORE_CFLAGS) \
+	$(NULL)
+
+LDADD = \
+	$(top_builddir)/src/libmsc/libmsc.a \
+	$(LIBOSMOCORE_LIBS) \
+	$(NULL)
+
+EXTRA_DIST = \
+	sdp_msg_test.ok \
+	sdp_msg_test.err \
+	$(NULL)
+
+noinst_PROGRAMS = \
+	sdp_msg_test \
+	$(NULL)
+
+sdp_msg_test_SOURCES = \
+	sdp_msg_test.c \
+	$(NULL)
+
+.PHONY: update_exp
+update_exp:
+	$(builddir)/sdp_msg_test >$(srcdir)/sdp_msg_test.ok 2>$(srcdir)/sdp_msg_test.err