Respect byteorder in StataReader

Partially fix pandas-dev#11282 for s390x

Author: aplanas

pandas/io/stata.py

@@ -1349,7 +1349,7 @@ def _read_strls(self):
                     buf = buf[0:2] + buf[4:10]
                 else:
                     buf = buf[0:2] + buf[6:]
-                v_o = struct.unpack('Q', buf)[0]
+                v_o = struct.unpack(self.byteorder + 'Q', buf)[0]
             typ = struct.unpack('B', self.path_or_buf.read(1))[0]
             length = struct.unpack(self.byteorder + 'I',
                                    self.path_or_buf.read(4))[0]