s3: Fix clear_if_first for the async echo handler

s3: Fix clear_if_first for the async echo handler

A worker smbd is as not long-lived as the main smbd, but as the async
echo handler exits when the worker smbd does, passing "true" here is the
right thing to do and fixes our clear_if_first handling when the async
echo handler is active.

Reviewed-by: Christian Ambach <ambi@samba.org>
Autobuild-User(master): Christian Ambach <ambi@samba.org>
Autobuild-Date(master): Fri Dec  7 11:29:36 CET 2012 on sn-devel-104