net: netcp: allocate buffers to desc before re-enable interrupt

Currently netcp_rxpool_refill() that refill descriptors and attached
buffers to fdq while interrupt is enabled as part of NAPI poll. Doing
it while interrupt is disabled could be beneficial as hardware will
not be starved when CPU is busy with processing interrupt.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>