link: refactor, reorder and fix bugs.

[MikeMcQuaid]

The change in #4441 broke the handling of the elsifs due to the change in logic. As every block here has a next there's no need to do an elsif in here at all. Additionally, reorder the conditions in here so you get an appropriate message depending on what you're trying to do. Finally, tweak some of the messaging to remove things that are ignored and tell people correct commands to run to link things.

References #4441 (comment)

CC @ilovezfs @DomT4

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

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[ilovezfs]

Thanks!

[DomT4]

Thanks Mike. Does indeed seem to resolve both the issues I was seeing locally.