EAP-pwd peer: Add support for hashed password

EAP-pwd peer: Add support for hashed password

This extends EAP-pwd peer support to allow NtHash version of password
storage in addition to full plaintext password. In addition, this allows
the server to request hashed version even if the plaintext password is
available on the client. Furthermore, unsupported password preparation
requests are now rejected rather than allowing the authentication
attempt to continue.

Signed-off-by: Jouni Malinen <j@w1.fi>