Currently, when the C driver writes the length of a document sequence payload in an OpMsg, it writes the length as native-endian instead of little-endian.

Here is the problematic line:
https://github.com/mongodb/mongo-c-driver/blob/e86e19589294b348ef8e7c547d65babb42fb089b/src/mongoc/mongoc-rpc.c#L116

Support for document sequences was added in the change below, and did the endian encoding correctly:
https://github.com/mongodb/mongo-c-driver/commit/c2073231209f20f5eef7263e969ae69ed47a031e
A regression in behavior was added in this change
https://github.com/mongodb/mongo-c-driver/commit/0f12b9d2782feef0418894bcd0134c89e21a5b5e