[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>

vllm_ascend/distributed/mooncake/transfer_engine.py

@@ -1,3 +1,4 @@
+import ipaddress
 import threading
 from typing import Optional
 
@@ -8,6 +9,15 @@ _global_te_lock = threading.Lock()
 
 
 def get_global_te(hostname: str, device_name: Optional[str]):
+    try:
+        ip = ipaddress.ip_address(hostname)
+        if isinstance(ip, ipaddress.IPv6Address):
+            raise RuntimeError(
+                "The backend if mooncake's Ascend Direct Xfer Library currcenly dose not support IPv6."
+            )
+    except ValueError:
+        pass
+
     global _global_te
     if _global_te is None:
         with _global_te_lock: