Use correct name-type in TGS-REQs for 2008R2 RODCs

Correctly set the name-type for the TGS principals to KRB5_NT_SRV_INST
in TGS-REQs.  (Previously, only AS-REQs had the name-type set in this
way.)  Windows Server 2008 R2 read-only domain controllers (RODCs)
insist on having the correct name-type for the TGS principal in
TGS-REQs as well as AS-REQs, at least for the TGT-forwarding case.

Thanks to Sebastian Galiano for reporting this bug and helping with
testing.

(cherry picked from commit 5994d8928b8ff88751b14bc60c7d7bfce8b30e57)

https://github.com/krb5/krb5/commit/7a9927270463a213f4af84462743315dcffd71d1
Author: Tom Yu <tlyu@mit.edu>
Commit: 7a9927270463a213f4af84462743315dcffd71d1
 src/lib/krb5/krb/fwd_tgt.c |   12 ++++--------
 src/lib/krb5/krb/tgtname.c |   19 +++++++++++++++----
 2 files changed, 19 insertions(+), 12 deletions(-)