move SRV check from models/dns.py to dns.py

[miesi]

    def create(name, type, view, ttl, comment=None, **kwargs):
        if type == 'SRV':
            labels = name.split('.')
            if len(labels) < 2 or not labels[0].startswith('_') or not labels[1].startswith('_'):
                raise InvalidParameterError('SRV records must start with two _ labels service and proto')
        kwargs = RR.validate_args(type, **kwargs)
        rr = RR(name=name, type=type, view=view, ttl=ttl, comment=comment)
        for field in list(kwargs.keys()):
            if field == 'ip':
                rr.ipblock = kwargs['ip']
            elif field in RRType.target_fields:
                rr.target = make_fqdn(kwargs[field], view.zone.name)
        rr.value = RR.get_class(type).value_from_fields(**kwargs)
        return rr