net: fib_rules ordering fixes.

We need to setup the network namespace state before we register
the notifier.  Otherwise if a network device is already registered
we get a nasty NULL pointer dereference.

Signed-off-by: Eric W. Biederman <ebiederm@maxwell.aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>