ipc_setup: Set SO_PASSCRED on listener socket

This is needed, because newer kernels doesn't correctly support setting
SO_PASSCRED on sockets returned by accept call, but socket option must
be set on server socket (before accept call).

For more details, see:
http://patchwork.ozlabs.org/patch/284366/

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Merge pull request #96 from jfriesse/master

ipc_setup: Set SO_PASSCRED on listener socket