net/mlx5: fix linkage of glue lib with gcc 4.7.2

net/mlx5: fix linkage of glue lib with gcc 4.7.2

addressing a gcc 4.7.2 bug that cannot be reproduced with latter
versions:

"bin/ld: Warning: alignment 8 of symbol `mlx5_glue' in
src/dpdk/drivers/net/mlx5/mlx5_glue.c.21.o is smaller than 16 in
src/dpdk/drivers/net/mlx5/mlx5_rxq.c.21.o"

Fix it be forcing the alignment of the glue lib.

Fixes: 0e83b8e536c1 ("net/mlx5: move rdma-core calls to separate file")
Cc: stable@dpdk.org
Signed-off-by: Yaroslav Brustinov <ybrustin@cisco.com>
Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>