BSC_Tests/hopping: fix bit-mask reduction in f_TC_fh_params_gen_tr_ma()

Change-Id: Id8b1e9fb62f9deaa5517d7366271437af0fc6eef
Related: SYS#4868, OS#4545
diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index 87e0d08..1b37f78 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -6918,7 +6918,7 @@
 	}
 
 	/* Ensure that ma_mask is octet-aligned */
-	ma_mask := substr(ma_mask, 0, ma_mask_len + 1);
+	ma_mask := substr(ma_mask, 0, ma_mask_len);
 	ma_mask_len := (ma_mask_len + 8 - 1) / 8;
 	ma_mask := f_pad_bit(ma_mask, ma_mask_len * 8, '0'B);