net/ipv6: reserve room for IFLA_INET6_ADDR_GEN_MODE
inet6_ifla6_size() is called to check how much space is needed by
inet6_fill_link_af() and inet6_fill_ifinfo(), both of which include
the IFLA_INET6_ADDR_GEN_MODE attribute. Reserve some room for it.
Fixes: d3e50a48d187 ("ipv6: addrconf: implement address generation modes") Signed-off-by: Sabrina Dubroca <sd@queasysnail.net> Reviewed-by: David Ahern <dsahern@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>