Add support for NETWORKING_WIFI_ADDRESS and NETWORKING_ETHERNET_ADDRESS

[schuyler]

Previously, the buendia-networking package was designed in such a way that two network interfaces could be defined (NETWORKING_ETHERNET_ADDRESS and NETWORKING_WIFI_ADDRESS) but only one IP address (NETWORKING_IP_ADDRESS).

This PR refactors the networking configuration script into shell functions -- hopefully, for clarity's sake -- and adds support for separate NETWORKING_WIFI_ADDRESS and NETWORKING_ETHERNET_ADDRESS configuration settings.

The expectation is that if an interface is defined but no static address is set, then the interface should attempt to acquire an address via DHCP.

The extant NETWORKING_IP_ADDRESS setting should be considered legacy, but it is still supported -- applied first to the Wi-Fi interface if no address is set for it, and then to the Ethernet interface if none is set for it.

STILL TODO:

• ~Thorough testing on an Intel NUC~
• ~Update site configs~
• ~Documentation update~

[zestyping]

Thanks! This looks great — all good with me. I would merge except that it's still marked "NOMERGE" so feel free to merge whenever you're ready!

[schuyler]

I'm just going to do one more round of testing on the NUC to be sure

[schuyler]

I've manually tested static and dynamic address allocation for wired and wireless interfaces on the NUC. I'm satisfied with how this works now, so I'm going to go ahead and merge.