private Version getVersion() {
        return version;
    }
Returns the (protocol) version of this network. This gets called when the "mbus.getVersion" method is invoked
on this network, and is separated into its own function so that unit tests can override it to simulate other
versions than current.

Note that this version reflects the highest supported <em>protocol</em> version, and is not necessarily
1-1 with the actual Vespa release version of the underlying binary.

@return the version to claim to be
messagebus/src/main/java/com/yahoo/messagebus/network/rpc/RPCNetwork.java