[NETNS]: Refactor fib initialization so it can handle multiple namespaces.

This patch makes the fib to be initialized as a subsystem for the
network namespaces. The code does not handle several namespaces yet,
so in case of a creation of a network namespace, the
creation/initialization will not occur.

Acked-by: Benjamin Thery <benjamin.thery@bull.net>
Acked-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/net/ip_fib.h
Simple merge

diff --cc net/ipv4/af_inet.c
Simple merge

diff --cc net/ipv4/fib_frontend.c
Simple merge

diff --cc net/ipv4/fib_hash.c
Simple merge

diff --cc net/ipv4/fib_rules.c
Simple merge

diff --cc net/ipv4/fib_trie.c
Simple merge