Add finish nni_list in struct nng_aio

1. Add finish nni_list in struct nng_aio.
2. Use a_finish_node to store finished aio in function sub0_recv_cb, thus separated from sub0_ctx recv_queue.

src/core/aio.h

@@ -209,6 +209,7 @@ struct nng_aio {
 	nni_aio_expire_q *a_expire_q;
 	nni_list_node     a_expire_node; // Expiration node
 	nni_reap_node     a_reap_node;
+	nni_list_node     a_finish_node; // Finished node
 };
 
 #endif // CORE_AIO_H

src/sp/protocol/pubsub0/sub.c

@@ -326,7 +326,7 @@ sub0_recv_cb(void *arg)
 		return;
 	}
 
-	nni_aio_list_init(&finish);
+	NNI_LIST_INIT(&finish, nng_aio, a_finish_node);
 
 	msg = nni_aio_get_msg(&p->aio_recv);
 	nni_aio_set_msg(&p->aio_recv, NULL);
@@ -388,6 +388,7 @@ sub0_recv_cb(void *arg)
 			nni_pollable_raise(&sock->readable);
 		}
 	}
+	nni_mtx_unlock(&sock->lk);
 
 	// NB: This is slightly less efficient in that we may have
 	// created an extra copy in the face of e.g. two subscriptions,
@@ -404,7 +405,6 @@ sub0_recv_cb(void *arg)
 		nni_list_remove(&finish, aio);
 		nni_aio_finish_sync(aio, 0, len);
 	}
-	nni_mtx_unlock(&sock->lk);
 
 	nni_pipe_recv(p->pipe, &p->aio_recv);
 }