Add SHA2 support to IKEv2 implementation

The following patch adds a stronger cryptographic suite to IKEv2 implementation.

The following algorithms can now be used for integrity checking in IKEv2 implementation (responder and initiator):
    - hmac-sha2-256-128
    - hmac-sha2-384-192
    - hmac-sha2-512-256

The default integrity checking method was set to hmac-sha2-256-128.

The default PRF function was set sha2-256.

Change-Id: Ia82b4cbbf3067b19b8487040dbefbaf4c9319548
Signed-off-by: Berenger Foucher <berenger.foucher@stagiaires.ssi.gouv.fr>