[NETNS]: Enable routing configuration in non-initial namespace.

I.e. remove the net != &init_net checks from the places, that now can
handle other-than-init net namespace.

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>