networking.7: Clarifications

+ standardize my license formatting with style guides
+ remove loading now-automatically loaded last-gen tethering driver
+ show contemporary internal hardware drivers for examples
+ tweak example language to hopefully improve clarity

MFC after: 3 days
Reviewed by: adrian, mhorne, Quentin Thebault
Approved by: mhorne (mentor)
Differential Revision: https://reviews.freebsd.org/D49762