This is an AES key size test to confirm conformance with RFC 3602 Section 5.3:

5.3. Key Length Attribute


   Since the AES allows variable key lengths, the Key Length attribute
   MUST be specified in both a Phase 1 exchange [IKE] and a Phase 2
   exchange [DOI].

We use ike=aes-sha1 and esp=aes-sha1

Current behaviour is expected to be:

1) allow aes128 and aes256 on the responder
2) use 128 on the initiator (it's the only mandatory to implement key size)

Previous behaviour was that for esp= we defaulted to 256 bit and for ike=
we didn't sent and key length (and we took that ourselves as to mean 128)

Future behaviour should be to send 2 proposals instead of one,
so this specification becomes symmetrial and will not break when
initiator/responder roles switch during rekey when only one end specfies
a specific key length.

NOTE: we support aes192, but it is not part of our default proposal. This
      is true for all our block cipihers.
