aue.4: Improve HARDWARE, specificity, and tag spdx

+ Improve HARDWARE introductory sentence for hardware release notes.
+ Mention "Fast" ethernet in title for apropos.
+ tag SPDX

MFC after: 3 days
Reviewed by: mhorne
Approved by: mhorne (mentor)
Differential Revision: https://reviews.freebsd.org/D50540

(cherry picked from commit 420e58595d20b6fd0dfdf2f486462fbb572f3351)