The first block response is unicast, and the client requests the further blocks
using unicast. https://tools.ietf.org/html/rfc7959#section-2.8
However, the hash for the server lookup of incoming data is based on
coap_addr_tuple_t which includes the local address - which changes between
receipt of mcast and unicast requests. This causes 2 sessions to be set up,
and the subsequent request/responses are treated as individual block random
access causing mismatch of information by the client.
Fix is to hash only on the remote address (IP + port) and local port for
servers.
Jon Shallow
50095d343a