Trace rnn max_batch_size (#17727)
Summary:
This causes the tracer to record the select / cast to int operation instead of just an int constant
Fixes #15319 but relies on a fix for #17583 first
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17727
Differential Revision: D14377886
Pulled By: driazati
fbshipit-source-id: 59453def54ba72756303f723993844dbeb5d2f8b
