MINOR: stconn: rename SE_FL_RXBLK_CONN to SE_FL_APPLET_NEED_CONN

This flag is exclusively used when a front applet needs to wait for the
other side to connect (or fail to). Let's give it a more explicit name
and remove the ambiguous function that was used only once.

This also ensures we will not risk to set it back on a new endpoint
after cs_reset_endp() via SE_FL_APP_MASK, because the flag being
specific to the endpoint only and not to the connector, we don't
want to preserve it when replacing the endpoint.
diff --git a/src/sink.c b/src/sink.c
index 831c5b4..6bd30fc 100644
--- a/src/sink.c
+++ b/src/sink.c
@@ -334,7 +334,7 @@
 	 */
 	if (cs_opposite(cs)->state < SC_ST_EST) {
 		cs_cant_get(cs);
-		cs_rx_conn_blk(cs);
+		se_need_remote_conn(appctx->sedesc);
 		cs_rx_endp_more(cs);
 		return;
 	}
@@ -474,7 +474,7 @@
 	 */
 	if (cs_opposite(cs)->state < SC_ST_EST) {
 		cs_cant_get(cs);
-		cs_rx_conn_blk(cs);
+		se_need_remote_conn(appctx->sedesc);
 		cs_rx_endp_more(cs);
 		return;
 	}