ipv6: remove unnecessary local variable

The local variable "struct net *net" in the two functions of
inet6_rtm_getaddr() and inet6_dump_addr() are actually useless,
so remove them.

Signed-off-by: Rocco Yue <rocco.yue@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>