include/ceph_fs.h: guard `#define CEPH_SETATTR_*` with #ifndef

include/ceph_fs.h: guard `#define CEPH_SETATTR_*` with #ifndef

this silences the warnings like:

```
from
/srv/autobuild-ceph/gitbuilder.git/build/out~/ceph-11.0.0-513-gfe98b0b/src/java/native/libcephfs_jni.cc:33:
warning:
/srv/autobuild-ceph/gitbuilder.git/build/out~/ceph-11.0.0-513-gfe98b0b/src/include/ceph_fs.h:373:0:
"CEPH_SETATTR_MODE" redefined [enabled by default]
^
In file included from
/srv/autobuild-ceph/gitbuilder.git/build/out~/ceph-11.0.0-513-gfe98b0b/src/java/native/libcephfs_jni.cc:32:0:
/srv/autobuild-ceph/gitbuilder.git/build/out~/ceph-11.0.0-513-gfe98b0b/src/include/cephfs/libcephfs.h:106:0:
note: this is the location of the previous definition
^
```

Signed-off-by: Kefu Chai <kchai@redhat.com>