igb: XDP extack message on error

Add an extack error message when the RX buffer size is too small
for the frame size.

Fixes: 9cbc948b

 ("igb: add XDP support")
Suggested-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Sven Auhagen <sven.auhagen@voleatech.de>
Tested-by: Sandeep Penigalapati <sandeep.penigalapati@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>