Merge branch 'ip_level_multicast_join_leave'

Merge branch 'ip_level_multicast_join_leave'

Madhu Challa says:

====================
Multicast group join/leave at ip level

This series enables configuring multicast group join/leave at ip level
by extending the "ip address" command.

It adds a new control socket mc_autojoin_sock and ifa_flag IFA_F_MCAUTOJOIN
to invoke the corresponding igmp group join/leave api.

Since the igmp group join/leave api takes the rtnl_lock the code had to
be refactored by adding a shim layer prefixed by __ that can be invoked
by code that already has the rtnl_lock. This way we avoid proliferation of
work queues.

The first patch in this series does the refactoring for igmp v6.
Its based on igmp v4 changes that were added by Eric Dumazet.

The second patch in this series does the group join/leave based on the
setting of the IFA_F_MCAUTOJOIN flag.

v5:
- addressed comments from Daniel Borkmann.
 - removed blank line in patch 1/2
 - removed unused variable, const arg in patch 2/2
v4:
- addressed comments from Yoshifuji Hideaki.
 - Remove WARN_ON not needed because we return a value from v2.
- addressed comments from Daniel Borkmann.
 - rename sock to mc_autojoin_sk
 - ip_mc_config() pass ifa so it needs one less argument.
 - igmp_net_{init|destroy}() use inet_ctl_sock_{create|destroy}
 - inet_rtm_newaddr() change scope of ret.
 - igmp_net_init() no need to initialize sock to NULL.
v3:
- addressed comments from David Miller.
 - fixed indentation and local variable order.
v2:
- addressed comments from Eric Dumazet.
 - removed workqueue and call __ip_mc_{join|leave}_group or
   __ipv6_sock_mc_{join|drop}
====================

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