Support Unix Domain Sockets in Golang TServerSocket

The existing API only supports opening TCP sockets. A minor change (in accordance with the existing API for TSocket) allows for use of unix domain sockets.

This will obviate the need for a library like this (https://github.com/Wang/thrift_unix_domain/blob/master/server_unix_domain.go) which is mostly a copy of the existing code with minor changes to support the domain socket.

Patch available: https://github.com/apache/thrift/pull/1284