These groups will contain socket-destruction events for
AF_INET/AF_INET6, IPPROTO_TCP/IPPROTO_UDP.

Near the end of socket destruction, a check for listeners is
performed.  In the presence of a listener, rather than completely
cleanup the socket, a unit of work will be added to a private
work queue which will first broadcast information about the socket
and then finish the cleanup operation.
Signed-off-by: NCraig Gallek <kraig@google.com>
Acked-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>