Robustness improvements to buendia-wifi-watchdog

[schuyler]

Some improvements to buendia-wifi-watchdog made while testing #247 in the hopes of making it more robust:

• skip running if no wifi interface is configured
• use iwconfig rather than wpa_cli to ensure that what we're looking at is network association, and ensure that wireless-tools is required by the package
• use ip to check that we actually have an IP address

Tested on the NUC by watching buendia-wifi-watchdog.log for several minutes, both with the network unconfigured and subsequently configured, to ensure the desired behavior. Also tested with and without a wifi interface defined. Performed same manual tests across multiple boots for confirmation.

[zestyping]

@schuyler Quick question here—why is iwconfig better than wpa_cli?

[schuyler]

@schuyler Quick question here—why is iwconfig better than wpa_cli?

The only good answer I have is that it works when wpa_supplicant isn't running, e.g. when the Wi-Fi network is open and doesn't require WPA security. This is not a use case the project currently has, at least not that I know of, but it was impossible for me to test the networking stack otherwise last week when the only Wi-Fi network I could use was an open one.

A less good answer is that iwconfig has been around longer and is more mature? But I wouldn't be sold on that myself per se.

Happy to take out this particular commit out of the PR if we're concerned about this choice.

[schuyler]

@zestyping bump for review?