mlx4: xdp_prog becomes inactive after ethtool '-L' or '-G'

After calling mlx4_en_try_alloc_resources (e.g. by changing the
number of rx-queues with ethtool -L), the existing xdp_prog becomes
inactive.

The bug is that the xdp_prog ptr has not been carried over from
the old rx-queues to the new rx-queues

Fixes: 47a38e15

 ("net/mlx4_en: add support for fast rx drop bpf program")
Cc: Brenden Blanco <bblanco@plumgrid.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>