TTLS: Fix peer challenge generation for TTLS/MSCHAPv2

TTLS: Fix peer challenge generation for TTLS/MSCHAPv2

Commit 30680e9332c96803533b9dae6105fd7b15b5bb52 changed the length
of the implicit challenge result to match with the exact length used
in TTLS. However, it failed to update the peer_challenge generation
to use a separate random value. Previously, this was generated as
part of the implicit challenge, but more correct way would have been
to generate a random value for it separately. Do this now to fix the
read after the allocated buffer (16 bytes after the implicit
challenge).

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>
intended-for: hostap-1