hv_netvsc: Set probe mode to sync

For better consistency of synthetic NIC names, we set the probe mode to
PROBE_FORCE_SYNCHRONOUS. So the names can be aligned with the vmbus
channel offer sequence.

Fixes: af0a5646 ("use the new async probing feature for the hyperv drivers")
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>