build: consolidate automake options to configure.ac

Also disable building the gzip distribution since we're building the
bzip2-compressed tarball already.

Signed-off-by: Diego Elio Pettenò <flameeyes@flameeyes.eu>
diff --git a/configure.ac b/configure.ac
index b85718b..101a1e8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2,7 +2,7 @@
 	m4_esyscmd([./git-version-gen .tarball-version]),
 	[openbsc@lists.osmocom.org])
 
-AM_INIT_AUTOMAKE([dist-bzip2])
+AM_INIT_AUTOMAKE([foreign dist-bzip2 no-dist-gzip 1.6])
 
 dnl kernel style compile messages
 m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])