ftmac100: use GFP_ATOMIC allocations where needed

When running in softirq context, we should use GFP_ATOMIC allocations
instead of GFP_KERNEL ones.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Tested-by: Po-Yu Chuang <ratbert@faraday-tech.com>
Acked-by: Po-Yu Chuang <ratbert@faraday-tech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>