Adds reduction args to signature of F.multilabel_soft_margin_loss docs (#70420)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/70301
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70420
Reviewed By: gchanan
Differential Revision: D33336924
Pulled By: jbschlosser
fbshipit-source-id: 18189611b3fc1738900312efe521884bced42666
