netutil/ifconfig: enable ipv6 autoconfig
netutil/ifconfig: enable ipv6 autoconfig

enable ipv6 autoconfig option.
it is disabled by default.
so user uses "ifconfig <interface_name> auto" this command,
it will enable the autoconfig option on that interface and
generate the link-local ipv6 address by autoconfig

Change-Id: I6055e52dbc48654eaa83ec97f0fa6ce6cc9d426b
Signed-off-by: jisuu.kim <800dec47d2987cee7cc3d7aee71bc11b56f5042e@samsung.com>

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