resolved: transaction - increase number of retry attempts

resolved: transaction - increase number of retry attempts

With the exponential backoff, we can perform more requests in the same amount of time,
so bump this a bit.

In case of large RTT this may be necessary in order not to regress, and in case
of large packet-loss it will make us more robust. The latter is particularly
relevant once we start probing for features (and hence may see packet-loss
until we settle on the right feature level).