MFS r320907: MFC r320906: MFV r320905: Import upstream fix for
CVE-2017-11103.

In _krb5_extract_ticket() the KDC-REP service name must be obtained
from encrypted version stored in 'enc_part' instead of the unencrypted
version stored in 'ticket'. Use of the unecrypted version provides an
opportunity for successful server impersonation and other attacks.

Submitted by: hrs
Obtained from: Heimdal
Security: FreeBSD-SA-17:05.heimdal
Security: CVE-2017-11103
Approved by: re (kib)