Add support for the psk_key_exchange_modes extension

This is required for the later addition of resumption support.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2259)

ssl/t1_trce.c

diff --git a/ssl/t1_trce.c b/ssl/t1_trce.c
index b3b6e18..9da8f75 100644
--- a/ssl/t1_trce.c
+++ b/ssl/t1_trce.c
@@ -449,6 +449,7 @@
     {TLSEXT_TYPE_server_authz, "server_authz"},
     {TLSEXT_TYPE_cert_type, "cert_type"},
     {TLSEXT_TYPE_key_share, "key_share"},
+    {TLSEXT_TYPE_psk_kex_modes, "psk_key_exchange_modes"},
     {TLSEXT_TYPE_supported_groups, "supported_groups"},
     {TLSEXT_TYPE_ec_point_formats, "ec_point_formats"},
     {TLSEXT_TYPE_srp, "srp"},
@@ -540,6 +541,11 @@
     {66, "ecdsa_fixed_ecdh"}
 };
 
+static ssl_trace_tbl ssl_psk_kex_modes_tbl[] = {
+    {TLSEXT_KEX_MODE_KE, "psk_ke"},
+    {TLSEXT_KEX_MODE_KE_DHE, "psk_dhe_ke"}
+};
+
 static ssl_trace_tbl ssl_crypto_tbl[] = {
     {TLS1_RT_CRYPTO_PREMASTER, "Premaster Secret"},
     {TLS1_RT_CRYPTO_CLIENT_RANDOM, "Client Random"},
@@ -760,6 +766,15 @@
         return ssl_trace_list(bio, indent + 2, ext + 1, xlen, 2,
                               ssl_version_tbl);
 
+    case TLSEXT_TYPE_psk_kex_modes:
+        if (extlen < 1)
+            return 0;
+        xlen = ext[0];
+        if (extlen != xlen + 1)
+            return 0;
+        return ssl_trace_list(bio, indent + 2, ext + 1, xlen, 1,
+                              ssl_psk_kex_modes_tbl);
+
     default:
         BIO_dump_indent(bio, (const char *)ext, extlen, indent + 2);
     }