[Cherry Pick from pr#3981][0.11.0][P/D]Make kv-transfer env variable take effect & Fix load-balance proxy (#3983)

### What this PR does / why we need it?
Make kv-transfer env variable take effect & Fix load-balance proxy.
Cherry Pick from #3981

---------
Signed-off-by: nwpu-zxr <zhouxuerong2@huawei.com>

vllm_ascend/distributed/llmdatadist_c_mgr_connector.py

@@ -30,6 +30,7 @@ from vllm.v1.core.sched.output import SchedulerOutput
 from vllm.v1.request import Request, RequestStatus
 
 import vllm_ascend.envs as envs_ascend
+from vllm_ascend.distributed.utils import get_transfer_timeout_value
 from vllm_ascend.utils import AscendSocVersion, get_ascend_soc_version
 
 TORCH_DTYPE_TO_NPU_DTYPE = {
@@ -411,7 +412,7 @@ class LLMDataDistCMgrConnectorWorker():
         assert self.local_agent_metadata is not None
         llm_config = LLMConfig()
         llm_config.device_id = self.local_rank
-        llm_config.sync_kv_timeout = 20000
+        llm_config.sync_kv_timeout = get_transfer_timeout_value()
         llm_config.enable_switch_role = True
         llm_config.enable_cache_manager = True
         llm_config.enable_remote_cache_accessible = True