netlink: fix ifaddr reporting.

Output the proper attributes for IPv4/IPvv6 ifaddrs:

• IFA_ADDRESS contains local address in every case except p2p, in that case it contains the peer address
• IFA_LOCAL contains local address. It is always present in IPv4, or in IPv6/p2p.
• IFA_BROADCAST contains the network broadcast address (if any)

Reported by: Adam Wood <aswood@gmail.com>
Tested by: Adam Wood <aswood@gmail.com>