Inspired by msg211764, issue20682

In short: 
   For address family of AF_UNIX or AF_UNIX_CCSID, getsockname() returns 0 if issued before a bind(). The address length is 0. This is always the case for sockets created by socketpair().

That is at least one possible explanation I found.

Have tested on AIX 6.1 and AIX 7.1 - transport.get_extra_info('sockname') returns None