Define an ifmedia_t type to use for ifmedia words.
Add ifconfig_media_lookup_* functions to lookup ifmedia words by name.
Get media options as an array of option names rather than formatting it
as a comma-delimited list into a buffer.
Sprinkle const on static the static description tables for peace of
mind.
Don't need to zero memory allocated by calloc.
Reviewed by: kp
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D29029
c4ba4aa547