The upstream behavior here changed, and the request needs a `nil`
instead of an empty slice to indicate that we _don't_ want to filter on
Network ACL IDs.
fixes#1634
Fixes the following vet reports:
builtin/providers/aws/resource_aws_network_acl.go:191: wrong number of args for format in Errorf call: 2 needed but 3 args
builtin/providers/aws/resource_aws_network_acl.go:264: wrong number of args for format in Errorf call: 1 needed but 2 args
builtin/providers/aws/resource_aws_network_acl.go:268: wrong number of args for format in Errorf call: 1 needed but 2 args
builtin/providers/aws/resource_aws_network_acl.go:286: arg m[to_port].(int) for printf verb %s of wrong type: int
builtin/providers/aws/resource_aws_network_acl_test.go:277: arg r.NetworkAcls for printf verb %s of wrong type: []github.com/mitchellh/goamz/ec2.NetworkAcl
builtin/providers/aws/resource_aws_subnet_test.go:21: arg v.MapPublicIpOnLaunch for printf verb %s of wrong type: bool
Clint Shryock