net/mlx4: fix missing initializers for old GCC

net/mlx4: fix missing initializers for old GCC

This patch works around compilation issues so far only seen on RHEL 7.2
using GCC 4.8.5:

 [...]/mlx4_rxq.c: In function `mlx4_rx_queue_setup':
 [...]/mlx4_rxq.c:473:3: error: missing initializer for field `ipackets' of
     `struct mlx4_rxq_stats' [-Werror=missing-field-initializers]

 [...]/mlx4_txq.c: In function `mlx4_tx_queue_setup':
 [...]/mlx4_txq.c:265:3: error: missing initializer for field `opackets' of
     `struct mlx4_txq_stats' [-Werror=missing-field-initializers]

Fixes: 79770826499b ("net/mlx4: drop live queue reconfiguration support")

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>