Drivers: hv: vmbus: define a new VMBus message type for hvsock

Drivers: hv: vmbus: define a new VMBus message type for hvsock

BugLink: http://bugs.launchpad.net/bugs/1541585
A function to send the type of message is also added.

The coming net/hvsock driver will use this function to proactively request
the host to offer a VMBus channel for a new hvsock connection.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 5c23a1a5c60b0f472cfa61cd7d8279f8aaeb5b64)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>