e, pending IPv6 DADs are not executed when the
device becomes ready.

I observed this while doing some tests with kvm. If I assign an IPv6 
address to my interface eth0 (kvm driver rtl8139) when it is still down
then the address is flagged tentative (IFA_F_TENTATIVE). Then, I set
eth0 up, and to my surprise, the address stays 'tentative', no DAD is
executed and the address can't be pinged.

I also observed the same behaviour, without kvm, with virtual interfaces
types macvlan and veth.

Some easy steps to reproduce the issue with macvlan:

1. ip link add link eth0 type macvlan
2. ip -6 addr add 2003::ab32/64 dev macvlan0
3. ip addr show dev macvlan0
   ... 
   inet6 2003::ab32/64 scope global tentative
   ...
4. ip link set macvlan0 up
5. ip addr show dev macvlan0
   ...
   inet6 2003::ab32/64 scope global tentative
   ...
   Address is still tentative

I think there's a bug in net/ipv6/addrconf.c, addrconf_notify():
addrconf_dad_run() is not always run when the interface is flagged IF_READY.
Currently it is only run when receiving NETDEV_CHANGE event. Looks like
some (virtual) devices doesn't send this event when becoming up.

For both NETDEV_UP and NETDEV_CHANGE events, when the interface becomes
ready, run_pending should be set to 1. Patch below.

'run_pending = 1' could be moved below the if/else block but it makes 
the code less readable.

Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
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