staging/lustre/lnet: fix potential null pointer dereference

Pointer 'ni' checked for NULL at line 1569 may be passed to
function and may be dereferenced there by passing argument 1 to
function 'lnet_ni_notify_locked' at line 1621.
found by Klocwork Insight tool

Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
CC: Dmitry Eremin <dmitry.eremin@intel.com>
CC: Liang Zhen <liang.zhen@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lnet/lnet/router.c

@@ -145,7 +145,7 @@ lnet_ni_notify_locked(lnet_ni_t *ni, lnet_peer_t *lp)
 	 * NB individual events can be missed; the only guarantee is that you
 	 * always get the most recent news */
 
-	if (lp->lp_notifying)
+	if (lp->lp_notifying || ni == NULL)
 		return;
 
 	lp->lp_notifying = 1;