Update SECJOIN tests

[Mališa Vučinić]

Current version of minimal-security is at -05, with -06 on the roadmap for May, before the plugtest.

This issue updates the SECJOIN tests in the TD referencing not-yet-published minimal-security-06 version, with the test semantics being sufficiently generic to cover the planned updates for -06.

[Mališa Vučinić]

Merged in malishav/td-6tisch/secjoin-06 (pull request #23)

Fix issue #28: Update to SECJOIN tests and typo fixing in L2SEC_01 test

Approved-by: Mališa Vučinić [e-mail]

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