Improve network connectivity dumping.

1. Explicitly dump IP addresses.

   Currently, some IP addresses are dumped using netcfg, but that
   only dumps the first IPv4 address on each interface. Instead,
   call ip -4 addr and ip -6 addr explicitly to dump all IPv4 and
   IPv6 addresses on the system.

2. Disable dumping /proc/net/{ipv6,}route, because:

 - We already dump all IPv4 and IPv6 routes in the tables that
   we use.
 - /proc/net/route is confusing because it only includes routes
   in the main table, which are all but unused. It's also in
   unreadable host-byte-order hex.
 - /proc/net/ipv6_route is confusing because it includes routes
   from all tables but does not say what table they are in.

3. Instead of dumping the contents of /proc/net/arp , use
   "ip -4 neigh show" and "ip -6 neigh show" to dump the
   neighbour caches for both IPv4 and IPv6.

Bug: 16663736
Change-Id: Id3e509b877ab7b00eb2399b6a9868b12245da2f0