Always set keepalive

Author: noamr

fetch.bs

@@ -6750,6 +6750,8 @@ is <a for="fetch group">deactivated</a>.
  <li><p>If <var>totalScheduledDeferredBytesForOrigin</var> is greater than 64 kilobytes, then
  throw a {{QuotaExceededError}}.
 
+ <li><p>Set <var>request</var>'s <a for=request>keepalive</a> to true.
+
  <li><p>Let <var>deferredRecord</var> be a new <a>deferred fetch record</a> whose
  <a for="deferred fetch record">request</a> is <var>request</var>.