L3_Templates: fix IMEI length: 14 (not 15)

The right length is 14. The 15th additional checksum digit is not
intended for digital transmission.

A good overview of the IMEI/IMEISV structure is here:
https://en.wikipedia.org/wiki/International_Mobile_Equipment_Identity#Structure_of_the_IMEI_and_IMEISV_(IMEI_software_version)

Related: Iaf2569c099874b55acbd748b776394726cc5ce54 (osmo-msc)
Change-Id: I7121f29a90f19d92c7bf26f26e76f1978c648459
diff --git a/library/L3_Templates.ttcn b/library/L3_Templates.ttcn
index a2fe67a..6af020b 100644
--- a/library/L3_Templates.ttcn
+++ b/library/L3_Templates.ttcn
@@ -2779,7 +2779,7 @@
 }
 
 function f_gen_imei(integer suffix) return hexstring {
-	return f_concat_pad(15, '49999'H, suffix);
+	return f_concat_pad(14, '49999'H, suffix);
 }
 
 function f_gen_imsi(integer suffix) return hexstring {