debian/libgtp6.shlibs: new file

List the most recent library version where new symbols where added, so
debian properly upgrades libgtp6 when upgrading osmo-sgsn from the
version that is currently in Debian to a version from the Osmocom
repositories.

Closes: OS#5318
Change-Id: Ida5dae4655c0acaeb377bc9d556a2ac333bca10a
diff --git a/debian/libgtp6.shlibs b/debian/libgtp6.shlibs
new file mode 100644
index 0000000..43d45e7
--- /dev/null
+++ b/debian/libgtp6.shlibs
@@ -0,0 +1,2 @@
+# Most recent version of the package that added new symbols (OS#5318)
+libgtp 6 libgtp6 (>= 1.8.0)