[codecs filter] add codec_filter.h,c

Add the infrastructure to store and filter all codec limitiations from
the different stages: MS, BSS, CN and remote call leg. Upcoming patches
will properly collect these and find an optimal codec.

No functional change, yet.

Related: SYS#5066
Change-Id: I4d90f7ca62f2307a7b93dd164aeecbf4bd98ff0a
diff --git a/src/libmsc/Makefile.am b/src/libmsc/Makefile.am
index c7fe4bb..bde70c9 100644
--- a/src/libmsc/Makefile.am
+++ b/src/libmsc/Makefile.am
@@ -27,6 +27,7 @@
 libmsc_a_SOURCES = \
 	call_leg.c \
 	cell_id_list.c \
+	codec_filter.c \
 	codec_mapping.c \
 	sccp_ran.c \
 	msc_vty.c \