overlay: create linkDir with mask 0755
overlay: create linkDir with mask 0755

on newer kernels we use idmapped mounts for the overlayfs.

When running in a user namespace that doesn't include the root user
from the host, the linDir cannot be accessed since CAP_DAC_OVERRIDE
doesn't work with IDs that are not part of the mapping.

To avoid this problem, create the linkDir with permissions 0755.

Closes: https://github.com/containers/storage/issues/1270

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

containers/storage,containers/storage,containers/storage