dpaa2-eth: Use napi_alloc_frag()

The driver is using netdev_alloc_frag() for allocation in the
->ndo_start_xmit() path. That one is always invoked in a BH disabled
region so we could also use napi_alloc_frag().

Use napi_alloc_frag() for skb allocation.

Cc: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Acked-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>