compilation fix for systems not supporting SKF_AD_VLAN_TAG_PRESENT
compilation fix for systems not supporting SKF_AD_VLAN_TAG_PRESENT

ntop/PF_RING,ntop/PF_RING,ntop/PF_RING,ntop/PF_RING,ntop/PF_RING,ntop/PF_RING,ntop/PF_RING