Add "iscsictl -M", which allows one to change session parameters
without removing it and adding back.

Sponsored by:	The FreeBSD Foundation
Rename a variable; no functional changes.

Sponsored by:	The FreeBSD Foundation
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
MFC after:	1 week