Re-set the gas settings for iterated client calls, fixing a bug with several activation paths

[jshufro]

This is a less-than-optimal but quick solution to https://github.com/rocket-pool/smartnode/issues/194

Optimally, the Client struct should be made less stateful. Users of the client interface should be required to pass the gas settings in at time of invocation, providing a compile-time enforcement that the settings are correctly derived.

I have only minimally tested this code.