Fix build wrt. missing CFLAGS constituents
When libosmo-netif and/or libosmo-abis are installed in distinct
prefixes, the build failed with non-found headers.
diff --git a/openbsc/src/libfilter/Makefile.am b/openbsc/src/libfilter/Makefile.am
index 4dbc590..ed3cd43 100644
--- a/openbsc/src/libfilter/Makefile.am
+++ b/openbsc/src/libfilter/Makefile.am
@@ -1,6 +1,6 @@
AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)
AM_CFLAGS=-Wall $(LIBOSMOCORE_CFLAGS) $(LIBOSMOGSM_CFLAGS) \
- $(LIBOSMOVTY_CFLAGS) $(LIBOSMOABIS_CFLAGS) $(COVERAGE_CFLAGS)
+ $(LIBOSMOVTY_CFLAGS) $(LIBOSMOABIS_CFLAGS) $(LIBOSMOSCCP_CFLAGS) $(COVERAGE_CFLAGS)
noinst_LIBRARIES = libfilter.a