[NET]: Remove unused define from loopback driver.

The LOOPBACK_OVERHEAD is not used in this file at all.
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/loopback.c

@@ -64,8 +64,6 @@ struct pcpu_lstats {
 	unsigned long bytes;
 };
 
-#define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
-
 /* KISS: just allocate small chunks and copy bits.
  *
  * So, in fact, this is documentation, explaining what we expect