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
Regenerate the list of generated symbols for libifconfig:
```
grep -hr ^ifconfig_sfp_ /usr/obj/usr/src/amd64.amd64/lib/libifconfig \
| sed 's/(.*/;/' | sort -u
```
Spotted by build failures caused by a missing symbol while working on
upgrading libifconfig from internal to private.
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D28927
This is a no-op for now since libifconfig is only built as a static lib.
Reviewed by: freqlabs, kp, adrian
Differential Revision: https://reviews.freebsd.org/D28119
