IPV6 is not advertived in registering consul-connect enabled services

### Nomad version
1.2.2

### Operating system and Environment details
Linux ubuntu 20.04

### Issue
To advertise ipv6 services with Consul, `advertise_ipv6_address` in docker config stanza and `address_mode = "driver"` in Consul service stanza are required to be set. However, It is not possible to set `address_mode` field for consul-connect services.

### Reproduction steps
1. Enable docker ipv6 in /etc/docker/daemon.json
{
"ipv6": true,
"fixed-cidr-v6": "2001:db8::/64"
}

2. Follow this [tutorial](https://www.nomadproject.io/docs/integrations/consul-connect) with a basic environment of nomad and consul.
3. Try to change the job spec from the same tutorial to enable ipv6 service advertisement by setting `advertise_ipv6_address` in docker config stanza and `address_mode = "driver"` in Consul service stanza.
4. Job submit will give error that `address_mode = "driver"` is not settable with service stanza in the group level.