[http] Unify criteria for split name

Add missing Etag from zendframework/zendframework#5302 c22ec11bf67f7d3f36edcd824ecdb26960c789d5

src/Header/Etag.php

@@ -20,7 +20,7 @@ public static function fromString($headerLine)
     {
         $header = new static();
 
-        list($name, $value) = explode(': ', $headerLine, 2);
+        list($name, $value) = GenericHeader::splitHeaderLine($headerLine);
 
         // check to ensure proper header type for this factory
         if (strtolower($name) !== 'etag') {