hyperv: Fix RNDIS send_completion code path

In some cases, the VM_PKT_COMP message can arrive later than RNDIS completion
message, which will free the packet memory. This may cause panic due to access
to freed memory in netvsc_send_completion().

This patch fixes this problem by removing rndis_filter_send_request_completion()
from the code path. The function was a no-op.

Reported-by: Long Li <longli@microsoft.com>
Tested-by: Long Li <longli@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>