library/Osmocom_Types: use f_rnd_bitstring() in f_rnd_ra11_ps()

Change-Id: I122d386b0c8ce320687016b6cab883b8a36bdffc
diff --git a/library/Osmocom_Types.ttcn b/library/Osmocom_Types.ttcn
index 967beb4..472b389 100644
--- a/library/Osmocom_Types.ttcn
+++ b/library/Osmocom_Types.ttcn
@@ -249,8 +249,7 @@
 
 /* generate a random 11-bit RA (packet-switched only) */
 function f_rnd_ra11_ps() return BIT11 {
-	var integer ra11 := f_rnd_int(bit2int('11111111111'B) + 1);
-	return int2bit(ra11, 11);
+	return f_rnd_bitstring(11);
 }