d/changelog: set epoch=1

Let apt know that the current 0.0.1 release of the split osmo-gbproxy
repository should be preferred over all packages from before the split.

Related: https://www.debian.org/doc/debian-policy/ch-controlfields.html#version
Change-Id: I3e3749cd14bff3b38261ae048b928ea8c54dfcef
diff --git a/debian/changelog b/debian/changelog
index c26fb12..06a570e 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,4 +1,4 @@
-osmo-gbproxy (0.0.1) unstable; urgency=medium
+osmo-gbproxy (1:0.0.1) unstable; urgency=medium
 
   [ Harald Welte ]
   * Further clean-up in osmo-sgsn -> osmo-gbproxy migration
@@ -11,7 +11,7 @@
 
  -- Oliver Smith <osmith@sysmocom.de>  Fri, 05 Feb 2021 11:42:48 +0100
 
-osmo-gbproxy (0.0.0) unstable; urgency=medium
+osmo-gbproxy (1:0.0.0) unstable; urgency=medium
 
   [ Neels Hofmeyr ]
   * manual: explain IuPS, add SCCP/M3UA section from common chapters