enable SA-based xattrs by default on new pools

These have been used pretty successfully for a number of years
in Core and SCALE. We can just enable by default these days and
get the corresponding performance boost.

src/middlewared/middlewared/plugins/pool_/pool.py

@@ -591,6 +591,7 @@ async def do_create(self, job, data):
             'acltype': 'posix',
             'compression': 'lz4',
             'aclinherit': 'passthrough',
+            'xattr': 'sa',
             'mountpoint': f'/{data["name"]}',
             **encryption_dict
         }