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/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index f825a62..8264f0e 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -349,7 +349,7 @@
 	struct net_device_context *ndevctx = netdev_priv(ndev);
 	struct hv_device *hdev =  ndevctx->device_ctx;
 	struct sockaddr *addr = p;
-	char save_adr[14];
+	char save_adr[ETH_ALEN];
 	unsigned char save_aatype;
 	int err;