memif: version 2

memif: version 2

In version 1 of the protocol sender was always ring producer and
receiver was consumer. In version 2 slave is always producer,
and in case of master-to-slave rings, slave is responsible for
populating ring with empty buffers.

As this is major change, we need to bump version number.

In addition, descriptor size is reduced to 16 bytes.

This change allows zero-copy-slave operation (to be privided in the separate
patch).

Change-Id: I02115d232f455ffc05c0bd247f7d03f47252cfaf
Signed-off-by: Damjan Marion <damarion@cisco.com>
Signed-off-by: Jakub Grajciar <jgrajcia@cisco.com>