net: macb: change GFP_ATOMIC to GFP_KERNEL

Now that the rx_fs_lock is no longer held across allocation, it's safe
to use GFP_KERNEL for allocating new entries.

This reverts commit 81da3bf6 ("net: macb: change GFP_KERNEL to
GFP_ATOMIC").

Cc: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Julia Cartwright <julia@ni.com>
Signed-off-by: David S. Miller <davem@davemloft.net>