IB/ipoib: Fix RCU pointer dereference of wrong object

Commit b63b70d8 ("IPoIB: Use a private hash table for path lookup
in xmit path") introduced a bug where in ipoib_neigh_free() (which is
called from a few errors flows in the driver), rcu_dereference() is
invoked with the wrong pointer object, which results in a crash.
Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/ipoib/ipoib_main.c

@@ -1052,7 +1052,7 @@ void ipoib_neigh_free(struct ipoib_neigh *neigh)
 	for (n = rcu_dereference_protected(*np,
 					    lockdep_is_held(&ntbl->rwlock));
 	     n != NULL;
-	     n = rcu_dereference_protected(neigh->hnext,
+	     n = rcu_dereference_protected(*np,
 					lockdep_is_held(&ntbl->rwlock))) {
 		if (n == neigh) {
 			/* found */