Push virNWFilterRuleInstPtr out of (eb|ip)tablesCreateRuleInstance
    
    Later refactoring will change use of the virNWFilterRuleInstPtr struct.
    Prepare for this by pushing use of the virNWFilterRuleInstPtr parameter
    out of the ebtablesCreateRuleInstance and iptablesCreateRuleInstance
    methods. Instead they simply string(s) with the constructed rule data.
    The ebiptablesCreateRuleInstance method will make use of the
    virNWFilterRuleInstPtr struct instead.
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>