Missing Data in LCP echo replies

[alexk99]

I've noticed that BNGBlaster 0.9.17 doesn't include the original Data payload when replying to LCP echo requests. I believe this is a bug. Although the RFC 1661 does not explicitly state that data must be copied, the common sense behind the echo logic requires that. Also, this behavior makes impossible tests like this https://datatracker.ietf.org/doc/html/rfc4638#section-5.2