Optimize multiplication in GF(2^k) used in OT extension

[GuutBoy]

In the current OT extension implementation a large amount of time is spent computing multiplications in GF(2^k) when computing inner products of vectors with entries in GF(2^k). It should be possible to optimize this computation.

The concrete method to optimize is RotSharedImpl.multiplyWithoutReduction(...).

On modern processors one could do this using the CLMUL instruction set, however, this does not seem to be immediately available in Java.