Avoid dialing known _local_ addresses when not in that network

[jbenet]

See #1226

Change p2p/net to avoid dialing known local area network addresses when not in that local network.

For example, it does not make sense to dial a 192.168.0.0/16 address when not within that subnet. This alone will cut out most -- if not all -- of the sysadmin netscan warnings. Most VPSes are in different networks.

We need to:

• identify a list of all subnets that we should do this with.
• implement the changes

[whyrusleeping]

my thoughts for a simple, "quick and easy" solution are to provide a config setting to allow users to specify which ranges to avoid dialing.

[Stebalien]

Moving to libp2p: libp2p/go-libp2p#436