kdc: allow checksum of PA-FOR-USER to be HMAC_MD5

kdc: allow checksum of PA-FOR-USER to be HMAC_MD5

even if the tgt session key uses different hmac.

Per [MS-SFU] 2.2.1 PA-FOR-USER the checksum is
always HMAC_MD5, and that's what windows 7 client
and MIT client send.

In heimdal both the client and kdc use the checksum of
the tgt key instead and therefore work with each other
but windows and MIT clients fail against heimdal KDC.

Windows KDC allows either checksum (HMAC_MD5 or from
tgt) so we should do the same to support all clients.

Signed-off-by: Isaac Boukris <iboukris@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Thu Jun 11 02:48:58 UTC 2020 on sn-devel-184