iavf: Restrict maximum VLAN filters for VIRTCHNL_VF_OFFLOAD_VLAN_V2

For VIRTCHNL_VF_OFFLOAD_VLAN, PF's would limit the number of VLAN
filters a VF was allowed to add. However, by the time the opcode failed,
the VLAN netdev had already been added. VIRTCHNL_VF_OFFLOAD_VLAN_V2
added the ability for a PF to tell the VF how many VLAN filters it's
allowed to add. Make changes to support that functionality.

Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>