net: macb: Change capability mask for jumbo support

JUMBO and NO_GIGABIT_HALF have the same capability masks.
Change one of them.

Signed-off-by: Harini Katakam <harinik@xilinx.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>