MEMNIC: new extra feature variable frame size

Design host and guest negotiation to enable extra feature in MEMNIC.
Use features and request (previous name reserved) fields to negotiate
between host and guest.

Here is the negotiation scenario;
Host sets provided extra feature bits, then guest can see which feature is available.
From guest, the driver will set request bit which want to be used in this session.
On reset timing, host checks requesting feature from guest and re-initialize MEMNIC
with the requested feature.

MEMNIC_FEAT_FRAME_SIZE is the new feature to support variable frame size
of MEMNIC interface in vSwitch.
Default frame size is the same as previous value,
MEMNIC_MAX_FRAME_LEN = 1518.
And the maximum value is MEMNIC_MAX_JUMBO_FRAME_LEN = 4088, which is
the maximum room size of MEMNIC packet data, 4096 - 8(meta data).

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Reviewed-by: Hayato Momma <h-momma@ce.jp.nec.com>