net: netsec: remove loops in napi Rx process

netsec_process_rx was running in a loop trying to process as many packets
as possible before re-enabling interrupts. With the recent DMA changes
this is not needed anymore as we manage to consume all the budget without
looping over the function.
Since it has no performance penalty let's remove that and simplify the Rx
path a bit

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>