logging: restrict sockets to mode 0600

logging: restrict sockets to mode 0600

The virtlogd daemon's only intended client is the libvirtd daemon. As
such it should never allow clients from other user accounts to connect.
The code already enforces this and drops clients from other UIDs, but
we can get earlier (and thus stronger) protection against DoS by setting
the socket permissions to 0600

Fixes CVE-2019-10132

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
(cherry picked from commit e37bd65f9948c1185456b2cdaa3bd6e875af680f)