net/mlx5: Consider RoCE cap before init RDMA resources

Check if RoCE is supported by the device before enable it in
the vport context and create all the RDMA steering objects.

Fixes: 80f09dfc ("net/mlx5: Eswitch, enable RoCE loopback traffic")
Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>