Set debhelper-compat version in Build-Depends.

Fixes lintian: uses-debhelper-compat-file
See https://lintian.debian.org/tags/uses-debhelper-compat-file.html for more details.

debian/compat

-12

debian/control

@@ -7,7 +7,7 @@ Uploaders: Arturo Borrero Gonzalez <arturo@debian.org>,
 Build-Depends: autoconf,
                automake,
                bison,
-               debhelper (>= 12~),
+               debhelper-compat (= 12),
                flex,
                libmnl-dev,
                libnetfilter-conntrack-dev,