mlx4: support __GFP_MEMALLOC for rx

Commit 04aeb56 ("net/mlx4_en: allocate non 0-order pages for RX
ring with __GFP_NOMEMALLOC") added code that appears to be not needed at
that time, since mlx4 never used __GFP_MEMALLOC allocations anyway.

As using memory reserves is a must in some situations (swap over NFS or
iSCSI), this patch adds this flag.

Note that this driver does not reuse pages (yet) so we do not have to
add anything else.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_rx.c

@@ -706,7 +706,8 @@ static bool mlx4_en_refill_rx_buffers(struct mlx4_en_priv *priv,
 	do {
 		if (mlx4_en_prepare_rx_desc(priv, ring,
 					    ring->prod & ring->size_mask,
-					    GFP_ATOMIC | __GFP_COLD))
+					    GFP_ATOMIC | __GFP_COLD |
+					    __GFP_MEMALLOC))
 			break;
 		ring->prod++;
 	} while (--missing);