contrib/fedora: Use pre-processing macros in spec file

...they seem to be supported by COPR now and make things simpler.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

contrib/fedora/rpkg.macros

@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+# PASST - Plug A Simple Socket Transport
+#  for qemu/UNIX domain socket mode
+#
+# PASTA - Pack A Subtle Tap Abstraction
+#  for network namespace/tap device mode
+#
+# contrib/fedora/rpkg.macros - rpkg macros (for COPR builds)
+#
+# Copyright (c) 2022 Red Hat GmbH
+# Author: Stefano Brivio <sbrivio@redhat.com>
+
+function git_version {
+	printf "0.git.%s.%s" "$(date -u -I | tr - _)" "$(git rev-parse --short HEAD)"
+}