Update Diffie-Hellman parameters to IANA standards

This replaces the old SKIP primes with the most current Diffie-Hellman
MODP groups defined by RFC 7296 and RFC 3526.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from GitHub https://github.com/openssl/openssl/pull/775)