gtp: Fix Makefile.am so maybe distcheck is now going to work
diff --git a/openbsc/include/openbsc/Makefile.am b/openbsc/include/openbsc/Makefile.am
index 15c38d1..d42f775 100644
--- a/openbsc/include/openbsc/Makefile.am
+++ b/openbsc/include/openbsc/Makefile.am
@@ -17,7 +17,7 @@
osmux.h mgcp_transcode.h gprs_utils.h utils.h \
gprs_gb_parse.h smpp.h meas_feed.h gprs_gsup_messages.h \
gprs_gsup_client.h bsc_msg_filter.h \
- oap.h oap_messages.h
+ oap.h oap_messages.h \
gtphub.h
openbsc_HEADERS = gsm_04_08.h meas_rep.h bsc_api.h