net/hyperv: fix wrong length of mac address

This patch fixed wrong mac length, it should be ETH_ALEN,
also replaced the hardcode 6 in hyperv_net.h

Signed-off-by: Amos Kong <kongjianjun@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index 5fd6f46..e6fe0d8 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -84,7 +84,7 @@
 };
 
 struct netvsc_device_info {
-	unsigned char mac_adr[6];
+	unsigned char mac_adr[ETH_ALEN];
 	bool link_state;	/* 0 - link up, 1 - link down */
 	int  ring_size;
 };