ixgbe: select pool by MAC when using double VLAN

ixgbe: select pool by MAC when using double VLAN

On X550, as required by datasheet, E-tag packets are not expected
when double VLAN are used. So modify the register PFVTCTL after
enabling double VLAN to select pool by MAC but not MAC or E-tag.

An introduction of E-tag:
It's defined in IEEE802.1br. Please reference this website,
http://www.ieee802.org/1/pages/802.1br.html.

A brief description.
E-tag means external tag, and it's a kind of l2 tunnel. It means a
tag will be inserted in the l2 header. Like below,
   |31            24|23           16|15         8|7           0|
  0|                   Destination MAC address                 |
  4|     Dest MAC address(cont.)    |     Src MAC address      |
  8|                  Source MAC address(cont.)                |
 12| E-tag Etherenet type (0x893f)  |      E-tag header        |
 16|                    E-tag header(cont.)                    |
 20|   VLAN Ethertype(optional)     |   VLAN header(optional)  |
 24|         Original type          |         ......           |
...|                              ......                       |
The E-tag format is like below,
   |0                    15|16   18|19 |20                   31|
   |   Ethertype - 0x893f  | E-PCP |DEI|   Ingress E-CID_base  |

   |32  33|34 35|36      47|48         55    |56             63|
   |  RSV | GRP |E-CID_base|Ingress_E-CID_ext|    E-CID_ext    |

The Ingess_E-CID_ext and E-CID_ext are always zero for endpoints
and are effectively reserved.

The more details of E-tag is in IEEE 802.1BR. 802.1BR is used to
replace 802.1Qbh. 802.1BR is a standard for Bridge Port Extension.
It specifies the operation of Bridge Port Extenders, including
management, protocols, and algorithms. Bridge Port Extenders
operate in support of the MAC Service by Extended Bridges.
The E-tag is added to l2 header to identify the VM channel and
the virtual port.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Shaopeng He <shaopeng.he@intel.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>
Tested-by: Yong Liu <yong.liu@intel.com>