misc: Fix python scripts shebang line

Type: fix

Since CentOS 8, RPM build script doesn't accept '#!/usr/bin/env python'
as a valid shebang line.  It requires scripts to explicitly chose
between python2 or python3.

Change all to use python3 as suggested by Paul Vinciguerra.

Depends-On: https://gerrit.fd.io/r/23170

Signed-off-by: Renato Botelho do Couto <renato@netgate.com>
Change-Id: Ie72af9f60fd0609e07f05b70f8d96e738b2754d1

test/test_geneve.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import socket
 from util import ip4_range, ip4_range