Set LayerNorm's eps to a number that is larger than 6e-5

[gejinchen]

Currently, many LayerNorm's eps are smaller than 6.1e-5 (smallest fp16 value), which might cause underflow.

[jimypbr]

@michaelbenayoun this is something that could be done easily as a torch.fx transform?

[michaelbenayoun]

I would think this is something handled by pytorch, but to answer you @jimypbr, yes definitely!