fuzzing: Break up handshake into more steps

Give the fuzzer a few more points to experiment with added branching
by explicitly using opt mode.

Message-Id: <20221006213452.3478687-1-eblake@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: "Richard W.M. Jones" <rjones@redhat.com>