[P/D] pd proxy support ipv6 (#4161)

### What this PR does / why we need it?
pd proxy support ipv6, mooncake connector check whether the IPv6 address
is used and notify the user.


- vLLM version: v0.11.0
- vLLM main:
2918c1b49c

---------

Signed-off-by: liziyu <liziyu16@huawei.com>

examples/disaggregated_prefill_v1/load_balance_proxy_server_example.py

@@ -88,6 +88,7 @@ import argparse
 import asyncio
 import functools
 import heapq
+import ipaddress
 import json
 import os
 import sys
@@ -117,7 +118,13 @@ class ServerState:
     def __init__(self, host, port):
         self.host = host
         self.port = port
-        self.url = f'http://{host}:{port}/v1'
+        ip = ipaddress.ip_address(self.host)
+        if isinstance(ip, ipaddress.IPv4Address):
+            self.url = f'http://{host}:{port}/v1'
+        elif isinstance(ip, ipaddress.IPv6Address):
+            self.url = f'http://[{host}]:{port}/v1'
+        else:
+            raise RuntimeError(f"Invild host IP address {ip}")
         self.client = httpx.AsyncClient(timeout=None,
                                         base_url=self.url,
                                         limits=httpx.Limits(
@@ -366,6 +373,8 @@ async def send_request_to_service(client: httpx.AsyncClient,
     req_data["stream"] = False
     req_data["max_tokens"] = 1
     req_data["min_tokens"] = 1
+    if "max_completion_tokens" in req_data:
+        req_data["max_completion_tokens"] = 1
     if "stream_options" in req_data:
         del req_data["stream_options"]
     headers = {