[dts] [dts 5/5] test_plans/vf_l3fwd_test_plan:update test plan to sync with testcase

[Ma, LihongX]

Regards,
Ma,lihong

> 
> +* Case config:
> +    For test vf_l3fwd perf, need to set "define RTE_TEST_RX_DESC_DEFAULT
> 2048" and "define RTE_TEST_TX_DESC_DEFAULT 20480"

Can you check the value RTE_TEST_TX_DESC_DEFAULT, I think it same as rx is 2048.