Update export.py with v3.0 Hardswish() support (#831)

models/export.py

@@ -7,6 +7,7 @@ Usage:
 import argparse
 
 import torch
+import torch.nn as nn
 
 from models.common import Conv
 from models.experimental import attempt_load
@@ -32,7 +33,7 @@ if __name__ == '__main__':
     # Update model
     for k, m in model.named_modules():
         m._non_persistent_buffers_set = set()  # pytorch 1.6.0 compatability
-        if isinstance(m, Conv):
+        if isinstance(m, Conv) and isinstance(m.act, nn.Hardswish):
             m.act = Hardswish()  # assign activation
         # if isinstance(m, Detect):
         #    m.forward = m.forward_export  # assign forward (optional)