[FS#361] git: add pre-receive hook to reject commits without SoB line

[LEDE Bugs]

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FS#361 - git: add pre-receive hook to reject commits without SoB line
User who did this: Ted Hess (thess)
Status: New -> Researching

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=361