After a brief moment of "Oh, Crap!" when both my WiFi and Ethernet stopped working this morning, it is now resolved.
WiFi mysteriously fixed itself after a third restart. Ethernet was resolved by installing the current version of IntelMausiEthernet.kext (2.4 as of this writing). While I was at it, I checked my other kexts and noted that FakeSMC.kext was also newer, so installed that (version 1800, and the associated sensor kexts) as well.