Add option to refrain from collecting IP addresses from disabled interfaces

[lunkwill42]

DeIC reports getting messages from Zino about IP addresses moving back and forth between interfaces. While this could be considered normal behavior in a VRRP setup (as evidenced by #215), since Zino doesn't understand VRRP, DeIC did not in fact have a VRRP setup.

Instead, DeIC has configured the same IP address on multiple router interfaces, but disabled all but one interface. Zino keeps claiming the IP address is jumping around between enabled and disabled interfaces.

The suggested fix is to ignore disabled interfacing when mapping IP addresses, but since @he32 doesn't seem to agree that DeICs config is reasonable, I suggest the compromise of adding this as an option that can be switched on/off in zino.toml