Initialize file permissions field for unix domain socket
Initialize file permissions field for unix domain socket

It seems like field->perm might be uninitialized memory
depending on how it is allocated.

I ran into an issue where different sockets had different file
permissions, and some of those sockets weren't readable by the user
which created it.

This behavior probably started in
https://github.com/twitter/twemproxy/pull/311/files

andyqzb/twemproxy,twitter/twemproxy,twitter/twemproxy,andyqzb/twemproxy,andyqzb/twemproxy,andyqzb/twemproxy,twitter/twemproxy,twitter/twemproxy