ionic: Use VLAN_ETH_HLEN when possible

Replace when ETH_HLEN and VLAN_HLEN are used together with
VLAN_ETH_HLEN since it's the same value and uses 1 define
instead of 2.

Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>