net: add helper eth_addr_add()

Add a helper to add an offset to a ethernet address. This comes in handy
if you have a base ethernet address for multiple interfaces.

Signed-off-by: Michael Walle <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Acked-by: Jakub Kicinski <[e-mail]>
Signed-off-by: Srinivas Kandagatla <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/linux/etherdevice.h

···
 }
 
 /**
+ * eth_addr_add() - Add (or subtract) an offset to/from the given MAC address.
+ *
+ * @offset: Offset to add.
+ * @addr: Pointer to a six-byte array containing Ethernet address to increment.
+ */
+static inline void eth_addr_add(u8 *addr, long offset)
+{
+	u64 u = ether_addr_to_u64(addr);
+
+	u += offset;
+	u64_to_ether_addr(u, addr);
+}
+
+/**
  * is_etherdev_addr - Tell if given Ethernet address belongs to the device.
  * @dev: Pointer to a device structure
  * @addr: Pointer to a six-byte array containing the Ethernet address