Update hardcoded DH parameters to IANA standards

The source defining the current fallback and hardcoded DH parameters
has disappeared from the web a long time ago, and RFC 3526 defines the
most current Diffie-Hellman MODP groups, so update to those new values.

Author: Daniel Gustafsson
Reviewed-by: Peter Eisentraut, Michael Paquier
Discussion: https://postgr.es/m/5E60AC9A-CB10-4851-9EF2-7209490A164C@yesql.se

src/include/libpq/libpq-be.h

@@ -206,19 +206,20 @@ typedef struct Port
  *	Hardcoded DH parameters, used in ephemeral DH keying.  (See also
  *	README.SSL for more details on EDH.)
  *
- *	If you want to create your own hardcoded DH parameters
- *	for fun and profit, review "Assigned Number for SKIP
- *	Protocols" (http://www.skip-vpn.org/spec/numbers.html)
- *	for suggestions.
+ *	This is the 2048-bit DH parameter from RFC 3526.  The generation of the
+ *	prime is specified in RFC 2412 Appendix E, which also discusses the
+ *	design choice of the generator.  Note that when loaded with OpenSSL
+ *	this causes DH_check() to fail on DH_NOT_SUITABLE_GENERATOR, where
+ *	leaking a bit is preferred.
  */
 #define FILE_DH2048 \
 "-----BEGIN DH PARAMETERS-----\n\
-MIIBCAKCAQEA9kJXtwh/CBdyorrWqULzBej5UxE5T7bxbrlLOCDaAadWoxTpj0BV\n\
-89AHxstDqZSt90xkhkn4DIO9ZekX1KHTUPj1WV/cdlJPPT2N286Z4VeSWc39uK50\n\
-T8X8dryDxUcwYc58yWb/Ffm7/ZFexwGq01uejaClcjrUGvC/RgBYK+X0iP1YTknb\n\
-zSC0neSRBzZrM2w4DUUdD3yIsxx8Wy2O9vPJI8BD8KVbGI2Ou1WMuF040zT9fBdX\n\
-Q6MdGGzeMyEstSr/POGxKUAYEY18hKcKctaGxAMZyAcpesqVDNmWn6vQClCbAkbT\n\
-CD1mpF1Bn5x8vYlLIhkmuquiXsNV6TILOwIBAg==\n\
+MIIBCAKCAQEA///////////JD9qiIWjCNMTGYouA3BzRKQJOCIpnzHQCC76mOxOb\n\
+IlFKCHmONATd75UZs806QxswKwpt8l8UN0/hNW1tUcJF5IW1dmJefsb0TELppjft\n\
+awv/XLb0Brft7jhr+1qJn6WunyQRfEsf5kkoZlHs5Fs9wgB8uKFjvwWY2kg2HFXT\n\
+mmkWP6j9JM9fg2VdI9yjrZYcYvNWIIVSu57VKQdwlpZtZww1Tkq8mATxdGwIyhgh\n\
+fDKQXkYuNs474553LBgOhgObJ4Oi7Aeij7XFXfBvTFLJ3ivL9pVYFxg5lUl86pVq\n\
+5RXSJhiY+gUQFXKOWoqsqmj//////////wIBAg==\n\
 -----END DH PARAMETERS-----\n"
 
 /*