REORG: thread/sched: move the last dynamic thread_info to thread_ctx

The last 3 fields were 3 list heads that are per-thread, and which are:
  - the pool's LRU head
  - the buffer_wq
  - the streams list head

Moving them into thread_ctx completes the removal of dynamic elements
from the struct thread_info. Now all these dynamic elements are packed
together at a single place for a thread.
diff --git a/src/h3.c b/src/h3.c
index 4540680..4acd95a 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -99,7 +99,7 @@
 	    unlikely((buf = b_alloc(&h3_uqs->qcs->tx.buf)) == NULL)) {
 		h3->buf_wait.target = h3_uqs;
 		h3->buf_wait.wakeup_cb = qcs_buf_available;
-		LIST_APPEND(&ti->buffer_wq, &h3->buf_wait.list);
+		LIST_APPEND(&th_ctx->buffer_wq, &h3->buf_wait.list);
 	}
 
 	return buf;