Interpret the media type from v1.1 protocol to support CDROM/DVD.

For v1.0 protocol, a disk's size continues to be calculated from the
geometry returned by the vdisk server. The geometry returned by the server
can be less than the actual number of sectors available in the backing
image/device due to the rounding in the division used to compute the
geometry in the vdisk server.

In v1.1 protocol a disk's actual size in sectors is returned during the
handshake. Use this size when v1.1 protocol is negotiated. Since this size
will always be larger than the former geometry computed size, disks created
under v1.0 will be forwards compatible to v1.1, but not vice versa.
Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>