main.c: add kdbus_msg_get_data()
test: some first steps for message sending
main: simplify kdbus_msg_get_data
main.c: add kdbus_msg_dump
main.c: add kdbus_msg_append_data
test-kdbus: cleanups
main.c: work towards kmsg-based implementation

The idea is to only hold a message inside a kmsg, so it's refcounted. It
won't change anyway, so we can simply enqueue the same kmsg at all
connections.
main.c: enqueue/dequeue logic
test-kdbus: simple polling on messages

Hey - breaking news! we can successfully play ping-pong now with
directed messages :)
main.c: re-order functions to get rid of forward-declarations
keep track of connections, implement message broadcasting
ep: convert to kref usage
bus: convert to kref
use u64 for internal data types, uint64_t is for userspace
move message code to own file
message: add KDBUS_MSG_DATA_SIZE

sizeof(struct kdbus_msg_data) is much bigger than it has to be in most
cases, due to the kdbus_cmd_name_info in the union.
message: only dequeue if copy_to_user was successful
names: first idea of a name lookup machine

entirely untested.
ep: register a name registry
remove old resolver stubs