Windows PV drivers fail to set up RSS when vCPU index >= 8

Windows PV drivers fail to set up RSS when vCPU index >= 8

The driver only supports at most 8 queues, however Windows
can decide to assign vCPU numbers starting from a non-zero
offset. E.g. vCPU 8,9,10,11 could get assigned to a device
if you have more than one NIC. The total number of vCPUs
used by a single device is still less than 8, but the vCPU
indexes themselves can be greater than 8. The code
previously incorrectly assumed that individual vCPU
indexes cannot exceed 8, however a 1:1 mapping between
vCPU indexes and queues seems to only exist when using
a single NIC.

Signed-off-by: Martin Harvey <martin.harvey@citrix.com>
Removed unncessary error handling and tidied up.

Signed-off-by: Paul Durrant <paul@xen.org>