### What this PR does / why we need it?
In fulldecodeonly mode, num_req_padded was set to an incorrect value,
causing accuracy degradation in Qwen3-Next. Therefore, we added a check
for compilation_config.cudagraph_mode to the conditional logic, ensuring
that padding is applied only in FULL mode.
### Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: v0.17.0
- vLLM main:
8a680463fa
Co-authored-by: wangxiaoxin-sherie <wangxiaoxin7@huawei.com>
cbf46fad3c