REORG: listener: move the listener's proto to the receiver

The receiver is the one which depends on the protocol while the listener
relies on the receiver. Let's move the protocol there. Since there's also
a list element to get back to the listener from the proto list, this list
element (proto_list) was moved as well. For now when scanning protos, we
still see listeners which are linked by their rx.proto_list part.
diff --git a/src/sock.c b/src/sock.c
index 161e723..8bdc3ea 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -363,7 +363,7 @@
 	int ns_namelen = 0;
 	int ret = -1;
 
-	if (!l->proto->addrcmp)
+	if (!l->rx.proto->addrcmp)
 		return -1;
 
 	/* WT: this is not the right way to do it, it is temporary for the
@@ -400,7 +400,7 @@
 #ifdef USE_NS
 		    (!ns_namelen || strcmp(l->bind_conf->settings.netns->node.key, xfer_sock->namespace) == 0) &&
 #endif
-		    l->proto->addrcmp(&xfer_sock->addr, &l->rx.addr) == 0)
+		    l->rx.proto->addrcmp(&xfer_sock->addr, &l->rx.addr) == 0)
 			break;
 		xfer_sock = xfer_sock->next;
 	}