lockd: Do not start the lockd thread before we've set nlmsvc_rqst->rq_task

This fixes an Oopsable race when starting lockd.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>