Linux ACL: default mask and default other

If an ACL has default values for `other` and `mask` these values will overwrite the non-default `other` and `mask` values.

E.g.:
```
# file: t
# owner: root
# group: root
user::rwx
user:www-data:rwx		#effective:---
group::r-x			#effective:---
mask::---
other::---
default:user::rwx
default:user:www-data:rwx
default:group::r-x
default:mask::rwx
default:other::---
```

Here the default `mask`/`other` values would overwrite the `mask`/`other` value.

This commit fixes that.