Use set_cached_acl and forget_cached_acl when possible

Use set_cached_acl and forget_cached_acl when possible

Originally, these two function are inline, so their usability is tied to
posix_acl_release. However, since Linux 3.14, they became EXPORT_SYMBOL, so we
can always use them. In this patch, we create an independent test for these
two functions so we can use them when possible.

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>