ggsn: Properly encode MISDN IE in GTP

ISDN-AddressString contains an initial byte at the start.
We didn't care so far because we were not yet checking the content of
msisdn, so the usual first '12'O byte was being considered as a header.

Let's store it in GTP format as before, but let's pass it as a
charstring when initializing the PdpContext, so that the human-style is
visible in the test for easy visualization/comparison (It will be
verified in a follow-up patch in Gy Diameter interface).

Change-Id: Ie1b65707d4b08f2201572e1fa44a1f9f985eb096
diff --git a/ggsn_tests/gen_links.sh b/ggsn_tests/gen_links.sh
index 6626467..c30e3da 100755
--- a/ggsn_tests/gen_links.sh
+++ b/ggsn_tests/gen_links.sh
@@ -10,6 +10,7 @@
 
 DIR=$BASEDIR/titan.Libraries.TCCUsefulFunctions/src
 FILES="TCCInterface_Functions.ttcn TCCConversion_Functions.ttcn TCCConversion.cc TCCInterface.cc TCCInterface_ip.h"
+FILES+=" TCCEncoding_Functions.ttcn TCCEncoding.cc " # BCD coding
 gen_links $DIR $FILES
 
 DIR=$BASEDIR/titan.TestPorts.Common_Components.Socket-API/src