### 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
"GuessMainPID": "yes",
            "IOScheduling": "0",
            "Id": "crond.service",
            "IgnoreOnIsolate": "no",
            "IgnoreOnSnapshot": "no",
            "IgnoreSIGPIPE": "yes",
            "InactiveEnterTimestampMonotonic": "0",
            "InactiveExitTimestamp": "Sun 2016-05-15 18:28:49 EDT",
            "InactiveExitTimestampMonotonic": "8135942",
            "JobTimeoutUSec": "0",
            "KillMode": "process",
            "KillSignal": "15",
            "LimitAS": "18446744073709551615",
            "LimitCORE": "18446744073709551615",
            "LimitCPU": "18446744073709551615",
            "LimitDATA": "18446744073709551615",
            "LimitFSIZE": "18446744073709551615",
            "LimitLOCKS": "18446744073709551615",
            "LimitMEMLOCK": "65536",
            "LimitMSGQUEUE": "819200",
            "LimitNICE": "0",
            "LimitNOFILE": "4096",
            "LimitNPROC": "3902",
            "LimitRSS": "18446744073709551615",
            "LimitRTPRIO": "0",
            "LimitRTTIME": "18446744073709551615",
            "LimitSIGPENDING": "3902",
            "LimitSTACK": "18446744073709551615",
            "LoadState": "loaded",
            "MainPID": "595",