bsdconfig: Add `network' keyword

Configuring a FreeBSD laptop, my fingers kept wanting to type
`bsdconfig network' and I could not figure out why this was not working.
Took me a second to realize that the shortcut was `bsdconfig networking'
for where I wanted to go.

Reviewed by: jhb
Approved by: jhb
Differential Revision: https://reviews.freebsd.org/D42242