cifs: Fix encoding of SMB1 Session Setup Kerberos Request in non-UNICODE mode

Like in UNICODE mode, SMB1 Session Setup Kerberos Request contains oslm and
domain strings.

Extract common code into ascii_oslm_strings() and ascii_domain_string()
functions (similar to unicode variants) and use these functions in
non-UNICODE code path in sess_auth_kerberos().

Decision if non-UNICODE or UNICODE mode is used is based on the
SMBFLG2_UNICODE flag in Flags2 packed field, and not based on the
capabilities of server. Fix this check too.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>