[FS#988] Procd does not respect a user's groups when using parameter user

[LEDE Bugs]

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FS#988 - Procd does not respect a user's groups when using parameter user
User who did this: Yousong Zhou (yousong)
Task Type: Bug Report -> Feature Request

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=988