### 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
the current user's scope C(user), or the scope of all users C(global).
            - "For systemd to work with 'user', the executing user must have its own instance of dbus started and accessible (systemd requirement)."
            - "The user dbus process is normally started during normal login, but not during the run of Ansible tasks.
              Otherwise you will probably get a 'Failed to connect to bus: no such file or directory' error."
            - The user must have access, normally given via setting the C(XDG_RUNTIME_DIR) variable, see example below.
        type: str
        choices: [ system, user, global ]
        default: system
        version_added: "2.7"
    no_block:
        description:
            - Do not synchronously wait for the requested operation to finish.
              Enqueued job will continue without Ansible blocking on its completion.
        type: bool
        default: no
        version_added: "2.3"
extends_documentation_fragment: action_common_attributes
attributes:
    check_mode:
        support: full
    diff_mode:
        support: none
    platform:
        platforms: posix
notes:
    - Since 2.4, one of the following options is required C(state), C(enabled), C(masked), C(daemon_reload), (C(daemon_reexec) since 2.8),
      and all except C(daemon_reload) and (C(daemon_reexec) since 2.8) also require C(name).
    - Before 2.4 you always required C(name).
    - Globs are not supported in name, i.e C(postgres*.service).
    - The service names might vary by specific OS/distribution