Document TCP as a valid listener protocol
Document TCP as a valid listener protocol

Seems TCP is missing from the list of valid values for listener protocol in the documentation (but is otherwise present in [code](https://github.com/terraform-providers/terraform-provider-aws/blob/1af53b1a47172733e1d6e233c29db6311107078d/aws/resource_aws_lb_listener.go#L265)).
charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws,ClementCunin/terraform-provider-aws,kjmkznr/terraform-provider-aws,nbaztec/terraform-provider-aws,kjmkznr/terraform-provider-aws,ClementCunin/terraform-provider-aws,kjmkznr/terraform-provider-aws,nbaztec/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,Ninir/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,terraform-providers/terraform-provider-aws,nbaztec/terraform-provider-aws,Ninir/terraform-provider-aws,ClementCunin/terraform-provider-aws,ClementCunin/terraform-provider-aws