Debian: package libgtp debug symbols as libgtp-dbg

... and some more Description for debian/control

Change-Id: I099735f8550134441a77c29e8c4d4d3c2490e379
diff --git a/debian/rules b/debian/rules
index 6f27da9..57fe24c 100755
--- a/debian/rules
+++ b/debian/rules
@@ -15,7 +15,8 @@
 	dh $@ --with autoreconf
 
 override_dh_strip:
-	dh_strip --dbg-package=osmo-ggsn-dbg
+	dh_strip -posmo-ggsn --dbg-package=osmo-ggsn-dbg
+	dh_strip -plibgtp2 --dbg-package=libgtp-dbg
 
 override_dh_autoreconf:
 	echo $(VERSION) > .tarball-version