igb: remove duplicated #include

Remove duplicated #include('s) in
  drivers/net/igb/igb_main.c

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/igb/igb_main.c

@@ -47,7 +47,6 @@
 #include <linux/if_ether.h>
 #include <linux/aer.h>
 #include <linux/prefetch.h>
-#include <linux/if_vlan.h>
 #ifdef CONFIG_IGB_DCA
 #include <linux/dca.h>
 #endif