Don't reject duplicate add if parms are identical

[ScottDaniels]

Currently if an add request is received for a VF/PF combination that is already in use VFd will reject the request. This is an enhancement request which asks that the parameters be examined and the add accepted if they are all the same.

Justification: some virtualisation managers seem to attempt to add a configuration when a guest is rebooted without first deleting it; it is felt that this is not a failure and thus VFd should not reject the request.