adjust clone url for nftables

Change-Id: I5052819a56ec9b856739b6529d49947bf83849e6
diff --git a/gen_makefile.py b/gen_makefile.py
index 573fd6b..0e0df10 100755
--- a/gen_makefile.py
+++ b/gen_makefile.py
@@ -171,7 +171,7 @@
 	touch $@
   '''
 
-  if proj in ("libgtpnl", "libnftnl"):
+  if proj in ("libgtpnl", "libnftnl", "nftables"):
     url = "git://git.netfilter.org"
 
   return f'''