net/hyperv: Use wait_event on outstanding sends during device removal

Change the busy-waiting/udelay to wait_event on outstanding sends.

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>