security: Fix hook iteration and default value for inode_copy_up_xattr

inode_copy_up_xattr returns 0 to indicate the acceptance of the xattr
and 1 to reject it. If the LSM does not know about the xattr, it's
expected to return -EOPNOTSUPP, which is the correct default value for
this hook. BPF LSM, currently, uses 0 as the default value and thereby
falsely allows all overlay fs xattributes to be copied up.

The iteration logic is also updated from the "bail-on-fail"
call_int_hook to continue on the non-decisive -EOPNOTSUPP and bail out
on other values.

Fixes: 98e828a0 ("security: Refactor declaration of LSM hooks")
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: James Morris <jmorris@namei.org>