ntlm: convert binary buffers to uint8_t *

ntlm: convert binary buffers to uint8_t *

Several binary buffers in the ntlm component are stored
as char *, however this generates a lot of warnings, because
hashing functions expect something unsigned.

Convert binary buffers to uint8_t *, while use explicit cast
for buffers that are really carrying a string inside.

This commit removes several warnings from ntlm.c that you can
catch with "-Wall -std=c99".

[DS: Done minor typo-fixes in commit message at commit time]

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Steffan Karger <steffan@karger.me>
Message-Id: <20170710043441.24770-2-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15032.html
Signed-off-by: David Sommerseth <davids@openvpn.net>
(cherry picked from commit e7e4070cb7b90f4836b65c53360166e11fc3f383)