gtphub: add to debian build

By the example of osmo-sgsn, package osmo-gtphub for debian.

Sponsored-by: On-Waves ehi
diff --git a/debian/rules b/debian/rules
index 8047b79..ee632a2 100755
--- a/debian/rules
+++ b/debian/rules
@@ -34,6 +34,7 @@
 	dh_strip -posmocom-sgsn --dbg-package=osmocom-sgsn-dbg
 	dh_strip -posmocom-gbproxy --dbg-package=osmocom-gbproxy-dbg
 	dh_strip -posmocom-bsc-nat --dbg-package=osmocom-bsc-nat-dbg
+	dh_strip -posmo-gtphub --dbg-package=osmo-gtphub-dbg
 
 override_dh_auto_configure:
 	echo $(VERSION) > openbsc/.tarball-version