Audit functions called during options_act_reversible()

While reviewing #4196 (moved), I wondered if it is actually safe to call parse_client_ports() from inside options_act_reversible(), because parse_client_ports() with its second argument set to 0 has a side effect. This shouldn't be allowed during options_act_reversible(), because we can't undo that change in the case of an error.

I suspect other issues like this may also exist. We should check to make sure all the functions don't modify state in a way we can't undo, or change the logic behind options_act_reversible() generally.