[dts][PATCH V1]test_plans/nic_single_core_perf: modify test plan to adapt meson build

[Tu, Lijuan]

> -    For FVL40g, if test 16 Byte Descriptor, need to set the
> "CONFIG_RTE_LIBRTE_I40E_16BYTE_RX_DESC=y"
> -    in ./config/common_base and re-build DPDK.
> 
> -    For CVL25G, if test 16 Byte Descriptor, need to set the
> "CONFIG_RTE_LIBRTE_ICE_16BYTE_RX_DESC=y"
> -    in ./config/common_base and re-build DPDK.
> -
> +    if test 16 or 32 Byte Descriptor, please set the value of
> +    "rx_desc_size" to 16 or 32 in dts/conf/nic_single_core_perf.cfg,
> +    and the default value is 16.

Test plan is to introduce feature, test cases and how to test manually, not how to use automation. 
If you would like to introduce that, welcome to contribute to guides in doc/gsg_dts/