Fix gamecontroller default network interface typo

[nycrat]

Description

In #3840, the new helper function to get the default network interface has a typo where it returns the ip instead of the interface. This works for some reason on ethernet but not when on wifi. This PR is just this one line fix.

Testing Done

Ran code on both wifi and ethernet. Everything works

Resolved Issues

N/A

Length Justification and Key Files to Review

N/A

Review Checklist

It is the reviewers responsibility to also make sure every item here has been covered

• Function & Class comments: All function definitions (usually in the .h file) should have a javadoc style comment at the start of them. For examples, see the functions defined in thunderbots/software/geom. Similarly, all classes should have an associated Javadoc comment explaining the purpose of the class.
• Remove all commented out code
• Remove extra print statements: for example, those just used for testing
• Resolve all TODO's: All TODO (or similar) statements should either be completed or associated with a github issue