net/mlx5: fix running without Rx queue

net/mlx5: fix running without Rx queue

When running mlx5_dev_start in mlx5_ethdev the function calls
mlx5_dev_configure_rss_reta in order to configure the rxq's.

Before mlx5_dev_configure_rss_reta there isn't a check whether
there are rxq's and if rxq's are 0 the function fails.
For example, this command:
/build/app/test-pmd/testpmd -n 4  -w 0000:08:00.0,rx_vec_en=0
-- --burst=64 --mbcache=512 -i  --nb-cores=27  --txd=2048 --rxd=2048
--vxlan-gpe-port=6081 --mp-alloc=xbuf --rxq 0 --forward-mode=txonly
would fail.

In order to fix this issue, we should call mlx5_dev_configure_rss_reta
only if we have rxq's.

Fixes: 63bd16292c3a ("net/mlx5: support RSS on hairpin")
Cc: stable@dpdk.org
Reported-by: Sylvain Rodon <srn@nexatech.fr>
Signed-off-by: Shiri Kuzin <shirik@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>