[NETNS][IPV6] addrconf - Pass the proper network namespace parameters to addrconf

This patch propagates the network namespace pointer to the address
configuration routines which need it, which means adding a new
parameter to these functions, and make them use it instead of using
the initial network namespace.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
Signed-off-by: David S. Miller <davem@davemloft.net>