Make TSocketAddress use folly::IPAddress

Make TSocketAddress use folly::IPAddress

Summary:
Step 1 of moving TAsyncSocket and friends to folly.

folly::IPAddress changes (can split these off if requested):
* isLoopback looks for a single address, as opposed to subnet
* For V6, isPrivate & isLoopback don't seem to check mapped addresses

TSocketAddress changes:
* Make union use folly::IPAddress instead of sockaddr struct.  external_ bool to tell if using AF_UNIX instead.
* manage the port and scope/zone info ourselves

@override-unit-failures

Overriding failures, can't get contbuild to finish all builds after several tries.  None of the failures look related

Test Plan:
fbconfig -r thrift
fbmake runtests
fbconfig folly/test:network_address_test
fbmake runtests

Reviewed By: simpkins@fb.com

Subscribers: snaptu-diffs@, trunkagent, hphp-diffs@, njormrod, fbcode-common-diffs@, doug, ruibalp, ps, alandau, bmatheny

FB internal diff: D1479365

Tasks: 3658665