nftables: Fix bug in NAT rule generation, D'oh.

Signed-off-by: Maximilian Wilhelm <max@sdn.clinic>

_modules/ffho_netfilter.py

@@ -147,7 +147,7 @@ def generate_nat_policy (roles, config_context):
 
 			for af in [ 4, 6 ]:
 				if str (af) in cc_nat[chain]:
-					np[4][chain] = cc_nat[chain][str (af)]
+					np[af][chain] = cc_nat[chain][str (af)]
 
 	return np