Merge branch 'net-Ease-to-follow-an-interface-that-moves-to-another-netns'

Nicolas Dichtel says:

====================
net: Ease to follow an interface that moves to another netns

The goal of this series is to ease the user to follow an interface that
moves to another netns.

After this series, with a patched iproute2:

$ ip netns
bar
foo
$ ip monitor link &
$ ip link set dummy0 netns foo
Deleted 5: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default
    link/ether 6e:a7:82:35:96:46 brd ff:ff:ff:ff:ff:ff new-nsid 0 new-ifindex 6

=> new nsid: 0, new ifindex: 6 (was 5 in the previous netns)

$ ip link set eth1 netns bar
Deleted 3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default
    link/ether 52:54:01:12:34:57 brd ff:ff:ff:ff:ff:ff new-nsid 1 new-ifindex 3

=> new nsid: 1, new ifindex: 3 (same ifindex)

$ ip netns
bar (id: 1)
foo (id: 0)
====================

Signed-off-by: David S. Miller <davem@davemloft.net>