cli: don't require "ifname" when adding connection
$ nmcli connection add type ethernet con-name t autoconnect no
Error: ifname argument is required.
This reverts commit a91eafdf ('cli: 'con add': make ifname mandatory (except bond,bridge,vlan) (bgo #698113'). Apparently this argument was required to avoid confusion (unexpected behavior). But I don't agree that is an issue, it's just annoying. Often you really have just one ethernet or Wi-Fi device, so this does not seem helpful.