cifs: have calc_lanman_hash take more granular args

We need to use this routine to encrypt passwords associated with the
tcon too. Don't assume that the password will be attached to the
smb_session.

Also, make some of the values in the lower encryption functions
const since they aren't changed.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>