etherdevice: introduce help function eth_zero_addr()

a lot of code has either the memset or an inefficient copy
from a static array that contains the all-zeros Ethernet address.
Introduce help function eth_zero_addr() to fill an address with
all zeros, making the code clearer and allowing us to get rid of
some constant arrays.
Signed-off-by: Duan Jiong <djduanjiong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/etherdevice.h

@@ -150,6 +150,17 @@ static inline void eth_broadcast_addr(u8 *addr)
 	memset(addr, 0xff, ETH_ALEN);
 }
 
+/**
+ * eth_zero_addr - Assign zero address
+ * @addr: Pointer to a six-byte array containing the Ethernet address
+ *
+ * Assign the zero address to the given address array.
+ */
+static inline void eth_zero_addr(u8 *addr)
+{
+	memset(addr, 0x00, ETH_ALEN);
+}
+
 /**
  * eth_hw_addr_random - Generate software assigned random Ethernet and
  * set device flag