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/osmo-bsc/Makefile.am b/openbsc/src/osmo-bsc/Makefile.am
index b4a2cba..69b363b 100644
--- a/openbsc/src/osmo-bsc/Makefile.am
+++ b/openbsc/src/osmo-bsc/Makefile.am
@@ -1,5 +1,5 @@
AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)
-AM_CFLAGS=-Wall $(LIBOSMOCORE_CFLAGS) $(LIBOSMOGSM_CFLAGS) $(LIBOSMOVTY_CFLAGS) $(LIBOSMOCTRL_CFLAGS) $(LIBOSMOSCCP_CFLAGS) $(COVERAGE_CFLAGS) $(LIBOSMOABIS_CFLAGS)
+AM_CFLAGS=-Wall $(LIBOSMOCORE_CFLAGS) $(LIBOSMOGSM_CFLAGS) $(LIBOSMOVTY_CFLAGS) $(LIBOSMOCTRL_CFLAGS) $(LIBOSMONETIF_CFLAGS) $(LIBOSMOSCCP_CFLAGS) $(COVERAGE_CFLAGS) $(LIBOSMOABIS_CFLAGS)
AM_LDFLAGS = $(COVERAGE_LDFLAGS)
bin_PROGRAMS = osmo-bsc