Enumerate supported DH parameters

[tyll]

The ServerKeyExchange message contains details about the DH parameters. It should be checked that it is complex enough.

[phibos]

The next version of FlexTLS can decode ServerKeyExchange messages. But at the moment I'm not sure how to check if the DH parameters are complex enough.

It's possible to extract three values from ServerDHParams.

• dh_p - The prime modulus used for the Diffie-Hellman operation.
• dh_g - The generator used for the Diffie-Hellman operation.
• dh_Ys - The server's Diffie-Hellman public value (g^X mod p).