Node to node connections should keep track of the nonce (iv)

[jumaffre]

To make sure that no replay attacks on encrypted forwarded requests from a backup to the primary can be performed, each node to node channel should keep track of the sender and receiver nonces (i.e. GCM IV) to check for continuity of messages sent.

This new mechanism should be resilient to loss of messages over the channel and reconnections. A unit test will probably be the best way to verify this behaviour.