[JTC] This set of cascading `if`-s should be refactored into something more readable.

[bmagyar]

This set of cascading if-s should be refactored into something more readable.
I suggest 2 things:

• make the selection of choosing the command somehow more explicit with different variable names, etc: tmp_command_ is not very intuitive
• refactor all the assign_interface_from_point uses into a function that gets a parameter, the command (whether it's desired state or the pid command)

Originally posted by @bmagyar in #225 (comment)

[christophfroehlich]

Investigate how to refactor these cascading ifs so that it is easier to read which conditions together lead to a failure.
This section of the code looks like a table of booleans where in some cases an error is flagged up.

Originally posted by @bmagyar in #225 (comment)