Linux 4.5 compat: Use xattr_handler->name for acl

Linux 4.5 compat: Use xattr_handler->name for acl

Linux 4.5 added member "name" to xattr_handler. xattr_handler which matches to
whole name rather than prefix should use "name" instead of "prefix".
Otherwise, kernel will return with EINVAL when it tries to resolve handlers.

Also, we remove the strcmp checks when xattr_handler has name, because
xattr_resolve_name will do the check for us.

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4549
Closes #4537