EAP-EKE: Add Session-Id

EAP-EKE: Add Session-Id

While RFC 6124 does not define how Session-Id is constructed for
EAP-EKE, there seems to be consensus among the authors on the
construction. Use this Type | Nonce_P | Nonce_S construction based on
the following email:

 From: Yaron Sheffer <yaronf.ietf at gmail.com>
 To: ietf at ietf.org
 Date: Wed, 17 Nov 2010 13:13:42 +0200

Expanding on my previous response, I suggest to resolve Bernard's
concern by adding the following text:

5.6 EAP Key Generation

EAP-EKE can be used for EAP key generation, as defined by [RFC 5247].
When used in this manner, the values required to establish the key
hierarchy are defined as follows:

- Peer-Id is the EAP-EKE ID_P value.
- Server-Id is the EAP-EKE ID_S value.
- Session-Id is the concatenated Type | Nonce_P | Nonce_S, where Type is
  the method type defined for EAP-EKE in [Sec. 4.1], a single octet.

Thanks,
	Yaron

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