Add GTP hub initial code base.

First steps towards a new GTP hub. The aim is to mux GTP connections, so that
multiple SGSN <--> GGSN links can pass through a single point. Background:
allow having more than one SGSN, possibly in various remote locations.

The recent addition of OAP to GSUP is related to the same background idea.

(This is a collapsed patch of various changes that do not make sense to review
in chronological order anymore, since a lot of it has thorougly transmorphed
after it was first committed.)

Sponsored-by: On-Waves ehf
diff --git a/openbsc/tests/testsuite.at b/openbsc/tests/testsuite.at
index 78aa47e..6a1c77f 100644
--- a/openbsc/tests/testsuite.at
+++ b/openbsc/tests/testsuite.at
@@ -110,3 +110,10 @@
 cat $abs_srcdir/oap/oap_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/oap/oap_test], [], [expout], [ignore])
 AT_CLEANUP
+
+AT_SETUP([gtphub])
+AT_KEYWORDS([gtphub])
+AT_CHECK([test "$enable_gtphub_test" != no || exit 77])
+cat $abs_srcdir/gtphub/gtphub_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/gtphub/gtphub_test], [], [expout], [ignore])
+AT_CLEANUP