MFC r267616:

Retooling addrconfig() to exclude addresses on loopback interfaces
when looking for configured addresses.
This change is based upon the code from the submitter, and made
following changes:
- Exclude addresses assigned on interfaces which are down, like NetBSD
  does.
- Exclude addresses assigned on interfaces which are ifdisabled.

PR:		190824
Submitted by:	Justin McOmie