[Core] Allow IPv6 in VLLM_HOST_IP with zmq (#8575)

Signed-off-by: Russell Bryant <rbryant@redhat.com>

vllm/utils.py

@@ -5,6 +5,7 @@ import datetime
 import enum
 import gc
 import inspect
+import ipaddress
 import os
 import random
 import socket
@@ -533,6 +534,14 @@ def get_ip() -> str:
     return "0.0.0.0"
 
 
+def is_valid_ipv6_address(address: str) -> bool:
+    try:
+        ipaddress.IPv6Address(address)
+        return True
+    except ValueError:
+        return False
+
+
 def get_distributed_init_method(ip: str, port: int) -> str:
     # Brackets are not permitted in ipv4 addresses,
     # see https://github.com/python/cpython/issues/103848