Drivers: hv: vmbus: briefly comment num_sc and next_oc

next_oc and num_sc fields of struct vmbus_channel deserve a description. Move
them closer to sc_list as these fields are related to it.

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>