d/changelog: generate entry for 1.6.1-2~bpo9+1 stretch-backports

A new changelog entry.

Git-Dch: Ignore
Signed-off-by: Arturo Borrero Gonzalez <arturo@debian.org>

debian/changelog

+iptables (1.6.1-2~bpo9+1) stretch-backports; urgency=medium
+
+  * Rebuild for stretch-backports.
+
+ -- Arturo Borrero Gonzalez <arturo@debian.org>  Mon, 13 Nov 2017 11:46:57 +0100
+
 iptables (1.6.1-2) unstable; urgency=medium
 
   [ Helmut Grohne ]