fix cell identifier generation in ttcn3 paging tests

The cell identifier used by the paging tests is 001-01, i.e. uses a
2-digit MNC. With the introduction of 3-digit MNC support in osmo-bsc,
the paging tests became incompatible with a osmo-bsc config with:

  network country code 1
  mobile network code 1

Explicitly declare a Cell_Identity with 2-digit MNC (includes an 'f').

Also, fix f_enc_mcc_mnc to properly encode 2-digit MNC values.

Related: OS#2847
Change-Id: Ide5228b403e43de8649b6eda18749ea2a9f592a9
diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index 972d912..2a05d26 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -949,7 +949,7 @@
 	GsmLac		lac,
 	GsmCellId	ci
 };
-private const Cell_Identity cid := { '001'H, '001'H, 1, 0 };
+private const Cell_Identity cid := { '001'H, 'f01'H, 1, 0 };
 
 type set of integer BtsIdList;