5133 Upstream SMB client fixes: Nexenta SUP-538 and SUP-548

@@ -180,17 +180,17 @@
 
         /*
          * If we have an IOD, it should immediately notice
          * that its connection has closed.  But in case
          * it doesn't, let's also send it a signal.
-         * (but don't shoot our own foot!)
-         * Note: the iod calls smb_iod_invrq on its way out.
          */
+        SMB_VC_LOCK(vcp);
         if (vcp->iod_thr != NULL &&
             vcp->iod_thr != curthread) {
                 tsignal(vcp->iod_thr, SIGKILL);
         }
+        SMB_VC_UNLOCK(vcp);
 }
 
 /*
  * Send one request.
  *