libifconfig: multiple feature additions
Added the ability to:
- Create virtual interfaces
- Create vlan interfaces
- Get interface fib
- Get interface groups
- Get interface status
- Get nd6 info
- Get media status
- Get additional ifaddr info in a convenient struct
- Get vhids
- Get carp info
- Get lagg and laggport status
- Iterate over all interfaces and ifaddrs
And add more examples, too.
Note that this is a backwards-incompatible change. But that's ok, because it's
a private library.
MFC after: 3 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D14463