why set layer0~4 to be eval() model twice?

[Hexuanfang]

Stereo-RCNN/lib/model/stereo_rcnn/resnet.py

Line 339 in 4d6dd65

self.RCNN_layer0.apply(set_bn_eval)

hi, thanks for your reading ahead, i got a confusion that why set self.RCNN_layer0.eval()
self.RCNN_layer1.eval() and what's the difference between line 316-317 and line 339-340?
looking forward to your reply!