Ensure trace recognises X25519

Using the -trace option to s_server or s_client was incorrectly printing
UNKNOWN for the X25519 curve.
Reviewed-by: NRich Salz <rsalz@openssl.org>

ssl/t1_trce.c

@@ -490,6 +490,7 @@ static ssl_trace_tbl ssl_curve_tbl[] = {
     {26, "brainpoolP256r1"},
     {27, "brainpoolP384r1"},
     {28, "brainpoolP512r1"},
+    {29, "ecdh_x25519"},
     {0xFF01, "arbitrary_explicit_prime_curves"},
     {0xFF02, "arbitrary_explicit_char2_curves"}
 };