audit: listen in all network namespaces

Convert audit from only listening in init_net to use register_pernet_subsys()
to dynamically manage the netlink socket list.

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

diff --cc kernel/audit.c
Simple merge

diff --cc kernel/audit.h
Simple merge

diff --cc kernel/auditfilter.c
Simple merge