How to use Netlink to get ipv6 neighbors

1. open netlink socket
2. send request to get neighbors
3. parse the response

The response is in the following format
[ netlink msg ] ... [ netlink msg ]

use the Macros defined in "man 3 netlink" to iterate through the messages. Each netlink message has a header "struct nlmsghdr *", defined in "man 7 netlink".

The netlink message for getting ipv6 neighbors is defined in "man 7 rtnetlink"

for ipv6 neighbors message, each netlink msg block has the following format:
  netlink-msg-header | neighbor-discover-msg-header (struct ndmsg) | route-attributes (struct rtattr) | more route-attributes...

Each route-attributes has the following format:
  header (struct rtattr) | data

The types of rtattr are defined in /usr/include/linux/neighbour.h, with the commons are:
  NDA_DST: data is IP address
  NDA_LLADDR: data is MAC address
  NDA_CACHEINFO: data is struct nda_cacheinfo


Example NetLink payload parsing (not showing nlmsghdr):

0a 00 00 00  :  inet family
02 00 00 00  : ifindex
04 00  : state
00 : flags
01 : type

14 00 : rtattr len
01 00 : type
fe 80 00 00 00 00 00 00 b6 ef fa ff fe d0 fe 76 : Ipv6 address

0a 00 : rtattr len
02 00 : type
b4 ef fa d0 fe 76 : mac

00 00  //padding

08 00  //probe ?
04 00
00 00 00 00

14 00 //rtattr len
03 00 //cache info
6b a8 e8 01 fb 90 e8 01
6b b9 69 00 00 00 00 00