Add support for IPv6 network setting

Add IPv6 setting in network setting page.
- Add IPv6 domain name, DNS servers, NTP servers enable/disable
- Add DHCPv6 enable/disable
- Add IPv6 default gateway

Add support for IPv6 network setting

Add IPv6 setting in network setting page.
- Add IPv6 domain name, DNS servers, NTP servers enable/disable
- Add DHCPv6 enable/disable
- Add IPv6 default gateway
- Add IPv6 addresses
- Add IPv6 static addresses
- Add IPv6 static addresses adding and deleting

Tested:
- IPv6 domain name, DNS servers, NTP servers enable/disable function
- DHCPv6 enable/disable function
- Verified the IPv6 default gateway
- IPv6 addresses adding and deleting
- Verified the IPv6 addresses in IPv6 table

Change-Id: I9eebf6ef5f7de748f79779d8168b8dcfcdda2495
Signed-off-by: Sean Zhang <xiazhang@nvidia.com>

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