while i can't follow exactly what you said local UNIX-domain sockets are different than remote Internet-domain ones
local sockets are sun_family AF_LOCAL/AF_UNIX and since they are local they only require a file path like
only processes running on the same machine can compunicate with a local namespace socket.
sockets connecting proceses over a network connection of any kind would have to be family PF_INET
and require aditional features like network transmition protocols machine names port numbers and junk like that.
this is from the bind() api description (BSD)
[ENOSYS] Function not implemented.
This error code is only returned on sockets that use the AF_UNIX or AF_UNIX_CCSID or AF_UNIX_CCSID address family.
not that that is alot of help but it does point to the fact that the function call is trying to implement a local not network socket.