client: Accept correctly spelled option name

Accept also correctly spelled version of 'preferred' option.
ipconfig: Use system set addresses for IPv4 property in 'manual' mode

Addresses and gateway for the service IPv4 property being used in the
system are available from ipconfig->system when the property is set to
'manual'.
service: Check service type before fetching interface index

For VPNs, the index is available from provider, for other services from
network.

Fixes BMC#26009
service: Update Domains property when Domains.Configuration changes

Domains property was not updated when Domains.Configuration was changed.
If Domains.Configuration is for example set to empty when using DHCP,
the Domains property is to be updated with the value configured via DHCP.

Fixes BMC#26010
test-ippool: Shortcut exhausting allocation test

Instead really trying to allocate all possible 69888 blocks, let's
reserve the first two IP pools and then we only need to allocate
255 blocks. That should bring down the runtime considerable.
vpn-config: Remove obsolete protected code

For VPN connections created via configuration files the immutable flag
is set and it ensures no modifications are allowed. The protected
feature implementation was a left-over from service configuration code.

Removing the code fixes a bug where only VPN entries of different types
can be provisioned in the same provisioning file.
vpn-config: Log a warning if the provider ident already exists

Also set the returned value appropriately when removing or adding
configuration files.
doc: Remove Protected description

The Protected setting was relevant only for Manager.ProvisionService
method call which was removed a long time ago.
config: Remove code implementing Protected config file setting

The code was relevant only for Manager.ProvisionService method call
which was removed a long time ago.
Release 1.15