[X25]: fix for spinlock recurse and spinlock lockup with timer handler

When the sk_timer function x25_heartbeat_expiry() is called by the
kernel in a running/terminating process, spinlock-recursion and
spinlock-lockup locks up the kernel.  This has happened with testing
on some distro's and the patch below fixed it.
Signed-off-by: NShaun Pereira <spereira@tusc.com.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/x25/x25_timer.c

@@ -114,8 +114,9 @@ static void x25_heartbeat_expiry(unsigned long param)
 			if (sock_flag(sk, SOCK_DESTROY) ||
 			    (sk->sk_state == TCP_LISTEN &&
 			     sock_flag(sk, SOCK_DEAD))) {
+				bh_unlock_sock(sk);
 				x25_destroy_socket(sk);
-				goto unlock;
+				return;
 			}
 			break;
 
@@ -128,7 +129,6 @@ static void x25_heartbeat_expiry(unsigned long param)
 	}
 restart_heartbeat:
 	x25_start_heartbeat(sk);
-unlock:
 	bh_unlock_sock(sk);
 }