When using umask 0077, the control interface directory was left without
group read/execute permissions even if the configuration file explicitly
asked for the group to be allowed to access the control interface. Fix
this by adding read/execute permissions for group if a specific group is
defined in the configuration. [Bug 199]
Removing just sun_family is not portable since some systems (e.g.,
FreeBSD) include an additional sun_len field. Using offsetof should be
portable. In addition, set sun_ken for FreeBSD.