MINOR: unix: use conn_full_close() instead of conn_force_close()

There's no point in using conn_force_close() in outgoing connect()
since XPRT_TRACKED is not set so both functions are equivalent.
diff --git a/src/proto_uxst.c b/src/proto_uxst.c
index 207bb00..4210f5d 100644
--- a/src/proto_uxst.c
+++ b/src/proto_uxst.c
@@ -557,7 +557,7 @@
 	fdtab[fd].linger_risk = 0;  /* no need to disable lingering */
 
 	if (conn_xprt_init(conn) < 0) {
-		conn_force_close(conn);
+		conn_full_close(conn);
 		conn->flags |= CO_FL_ERROR;
 		return SF_ERR_RESOURCE;
 	}