netfilter: nf_log: wait for rcu grace after logger unregistration

The nf_log_unregister() function needs to call synchronize_rcu() to make sure
that the objects are not dereferenced anymore on module removal.

Fixes: 5962815a ("netfilter: nf_log: use an array of loggers instead of list")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_log.c

@@ -117,6 +117,7 @@ void nf_log_unregister(struct nf_logger *logger)
 			RCU_INIT_POINTER(loggers[i][logger->type], NULL);
 	}
 	mutex_unlock(&nf_log_mutex);
+	synchronize_rcu();
 }
 EXPORT_SYMBOL(nf_log_unregister);