iavf: Change GFP_KERNEL to GFP_ATOMIC in kzalloc()

iavf_add_vlan() is being called in atomic context
so kzalloc() needs GFP_ATOMIC. This patch fixes it.

Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>