This test determines what happens if the R1 message is duplicated for some
reason.  In IKEv2, the initiator is responsible for all retransmissions, so
the initiator should not respond in any interesting way to a duplicate R1
message.  Such a message was either duplicated on the way back by the
network, or is the result of the responder having received two I1 messages
(perhaps one was a retransmission), and having replied twice.
