### Summary

when i use ansible systemd module, but the result is different between using systemd module and not using systemd module. 


```
 - name: using systemd module
    systemd:
      name: my.service
      state: stopped
      enabled: no
```

```
- name: using just command stop
  command: systemctl stop my.service

- name: using just command disable
  command: systemctl disable my.service
```
In Detail, my.service's killMode is process (KillMode=process), so if i stop my.service, another process in my.service cgroup  are not killed.  but when i use systemd module to stop and disable,  all process in my.service cgroup are killed 

### Issue Type

Bug Report

### Component Name

systemd

### Ansible Version

```console
$ ansible --version
ansible [core 2.11.10] 
  config file = /Users/kakao_ent/cloudms/git_ms/msg-deploy/ansible/ansible.cfg
  configured module search path = ['/Users/kakao_ent/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /Users/kakao_ent/cloudms/git_ms/msg-deploy/ansible/env/lib/python3.7/site-packages/ansible
  ansible collection location = /Users/kakao_ent/.ansible/collections:/usr/share/ansible/collections
  executable location = env/bin/ansible
  python version = 3.7.8 (v3.7.8:4b47a5b6ba, Jun 27 2020, 04:47:50) [Clang 6.0 (clang-600.0.57)]
  jinja version = 3.1.1
  libyaml = True
```


### Configuration

```console
# if using a version older than ansible-core 2.12 you should omit the '-t all'
$ ansible-config dump --only-changed -t all
```


### OS / Environment

Ubuntu 18.04

### Steps to Reproduce

1. not working task
```
 - name: using systemd module
    systemd:
      name: my.service
      state: stopped
      enabled: no
```

2. working task
```
- name: using just command stop
  command: systemctl stop my.service

- name: using just command disable
  command: systemctl disable my.service
```

and the service file attribute have to add like this

`KillMode=process`



### Expected Results

same as summary

### Actual Results

```console
same as summary
```


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
if 'ActiveState' in result['status']:
                action = None
                if module.params['state'] == 'started':
                    if not is_running_service(result['status']):
                        action = 'start'
                elif module.params['state'] == 'stopped':
                    if is_running_service(result['status']) or is_deactivating_service(result['status']):
                        action = 'stop'
                else:
                    if not is_running_service(result['status']):
                        action = 'start'
                    else:
                        action = module.params['state'][:-2]  
                    result['state'] = 'started'
                if action:
                    result['changed'] = True
                    if not module.check_mode:
                        (rc, out, err) = module.run_command("%s %s '%s'" % (systemctl, action, unit))
                        if rc != 0:
                            module.fail_json(msg="Unable to %s service %s: %s" % (action, unit, err))
            
            elif is_chroot(module) or os.environ.get('SYSTEMD_OFFLINE') == '1':
                module.warn("Target is a chroot or systemd is offline. This can lead to false positives or prevent the init system tools from working.")
            else:
                
                module.fail_json(msg="Service is in unknown state", status=result['status'])
    module.exit_json(**result)
if __name__ == '__main__':
    main()