python: Drop use of types.FunctionType.

This code asserted that the callback argument was of type
types.FunctionType.  It's more pythonic to just check that the argument
is callable, and not specifically that it's a function.  There are other
ways to implement a callback than types.FunctionType.

Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>

python/ovs/unixctl/__init__.py

@@ -12,8 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import types
-
 import six
 
 import ovs.util
@@ -63,7 +61,7 @@ def command_register(name, usage, min_args, max_args, callback, aux):
     assert isinstance(usage, strtypes)
     assert isinstance(min_args, int)
     assert isinstance(max_args, int)
-    assert isinstance(callback, types.FunctionType)
+    assert callable(callback)
 
     if name not in commands:
         commands[name] = _UnixctlCommand(usage, min_args, max_args, callback,