Add X25519 curve to list

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Emilia Käsper <emilia@openssl.org>

crypto/ec/ec_curve.c

diff --git a/crypto/ec/ec_curve.c b/crypto/ec/ec_curve.c
index befe59d..a95d519 100644
--- a/crypto/ec/ec_curve.c
+++ b/crypto/ec/ec_curve.c
@@ -3020,6 +3020,7 @@
      "RFC 5639 curve over a 512 bit prime field"},
     {NID_brainpoolP512t1, &_EC_brainpoolP512t1.h, 0,
      "RFC 5639 curve over a 512 bit prime field"},
+    {NID_X25519, NULL, ec_x25519_meth, "X25519"},
 };
 
 #define curve_list_length OSSL_NELEM(curve_list)