e1000: Improve device name strings

This is just clerical work to ease bug triage and may be used to set
expectations around the ability for anyone in the community to perform
testing and development on older parts (this driver covers over 20 years
of silicon)

Reviewed by: erj
Approved by: markj
Sponsored by: Pink Floyd - Any Colour You Like (in kind)
Differential Revision: https://reviews.freebsd.org/D29872