net: ipv6: send unsolicited NA if enabled for all interfaces

commit fc1f8f4f upstream.

When arp_notify is set to 1 for either a specific interface or for 'all'
interfaces, gratuitous arp requests are sent. Since ndisc_notify is the
ipv6 equivalent to arp_notify, it should follow the same semantics.
Commit 4a6e3c5d ("net: ipv6: send unsolicited NA on admin up") sends
the NA on admin up. The final piece is checking devconf_all->ndisc_notify
in addition to the per device setting. Add it.

Fixes: 5cb04436 ("ipv6: add knob to send unsolicited ND on link-layer address change")
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/ipv6/ndisc.c

@@ -1608,7 +1608,8 @@ static int ndisc_netdev_event(struct notifier_block *this, unsigned long event,
 		idev = in6_dev_get(dev);
 		if (!idev)
 			break;
-		if (idev->cnf.ndisc_notify)
+		if (idev->cnf.ndisc_notify ||
+		    net->ipv6.devconf_all->ndisc_notify)
 			ndisc_send_unsol_na(dev);
 		in6_dev_put(idev);
 		break;