`fused_Conv_Sigmoid_Mul` does not codegenerate

[matteoroda05]

Problem

fused_Conv_Sigmoid_Mul does not code-generate

Solution

1. Check if there is any missing code needed for the codegen (e.g. the actual operation in the core), fix and add that code;
2. Add the codegen;
3. Add the operator to the list of operators (if missing)l;
4. Test the operator using the -Dfused flag during testing (if no model currently uses some of these operators, find one that does).