Improve Docker and Kubernetes support for KNX

[plomosits]

Proposed change

Improve Docker and Kubernetes support for KNX by adding new XKNX parameter "route_back" to Home-Assistant configuration.
With this small change it is possible to use Home-Assistant with KNX on Kubernetes.
It is also possible to run Home-Assistant with KNX on a Docker host without using "network=host" as described at https://www.home-assistant.io/installation/linux#install-home-assistant-container

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example entry for configuration.yaml:

# Example configuration.yaml
knx:
  tunneling:
    host: '192.168.0.xxx'
    local_ip: '0.0.0.0'
    route_back: true

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

The integration reached or maintains the following Integration Quality Scale:

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To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[homeassistant]

Hi @plomosits,

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[probot-home-assistant]

Hey there @Julius2342, @farmio, @marvin-w, mind taking a look at this pull request as its been labeled with an integration (knx) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[agners]

This looks good to me but needs a documentation update in https://github.com/home-assistant/home-assistant.io/blob/current/source/_integrations/knx.markdown.

[frenck]

Documentation PR is open, it needs a rebase, but will keep track on that from the docs repo.

✅ LGTM, merging this end.