Fix setup of Huawei LTE for which we can't get a MAC address

[scop]

Description:

Don't specify None mac as device connection.

Related issue (if applicable): fixes #29188

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist

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• Documentation added/updated in home-assistant.io

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• Tests have been added to verify that the new code works.