At larger tx sizes (e.g. > 10000) we were spending non-neglible
amounts of time in tx creation, due to making the final bytes random.
The slower the send loop, the less accurate it is at measuring the time
tendermint took. (As we can't reach the promised contract of the given rate)
There really isn't much need for that randomness, so this PR makes it
such that only the txNumber gets bumped between txs from the same
connection, thereby improving sendloop speed and accuracy.
ValarDragon