Drivers: hv: vmbus: distribute subchannels among all vcpus

Drivers: hv: vmbus: distribute subchannels among all vcpus

Primary channels are distributed evenly across all vcpus we have. When the host
asks us to create subchannels it usually makes us num_cpus-1 offers and we are
supposed to distribute the work evenly among the channel itself and all its
subchannels. Make sure they are all assigned to different vcpus.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit ce59fec836a9b4dc51cbcf9cb245b59e0ef53bea)

Orabug: 21886720
Signed-off-by: Jason Luo <zhangqing.luo@oracle.com>