netrom: Fix a data-race around sysctl_netrom_transport_maximum_tries

We need to protect the reader reading the sysctl value because the
value can be changed concurrently.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: JasonXing

net/netrom/af_netrom.c

@@ -457,7 +457,7 @@ static int nr_create(struct net *net, struct socket *sock, int protocol,
 	nr->t2     =
 		msecs_to_jiffies(sysctl_netrom_transport_acknowledge_delay);
 	nr->n2     =
-		msecs_to_jiffies(sysctl_netrom_transport_maximum_tries);
+		msecs_to_jiffies(READ_ONCE(sysctl_netrom_transport_maximum_tries));
 	nr->t4     =
 		msecs_to_jiffies(sysctl_netrom_transport_busy_delay);
 	nr->idle   =