[NETNS]: Show routing information from correct namespace (fib_trie.c)

This is the second part (for the CONFIG_IP_FIB_TRIE case) of the patch
#4, where we have created proc files in namespaces.

Now we can dump correct info in them.

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>