Add ecc extensions only if ecc ciphersuite is used

Fix compliancy to RFC4492. ECC extensions should be included
only if ec ciphersuites are used. Interoperability issue with
bouncy castle. #1157
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index e537f9d..ad11292 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -766,6 +766,10 @@
     unsigned char offer_compress;
     const int *ciphersuites;
     const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
+#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+    int uses_ec = 0;
+#endif
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write client hello" ) );
 
@@ -917,6 +921,11 @@
         MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, add ciphersuite: %04x",
                                     ciphersuites[i] ) );
 
+#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+        uses_ec |= mbedtls_ssl_ciphersuite_uses_ec( ciphersuite_info );
+#endif
+
         n++;
         *p++ = (unsigned char)( ciphersuites[i] >> 8 );
         *p++ = (unsigned char)( ciphersuites[i]      );
@@ -1010,11 +1019,14 @@
 
 #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
     defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
-    ssl_write_supported_elliptic_curves_ext( ssl, p + 2 + ext_len, &olen );
-    ext_len += olen;
+    if( uses_ec )
+    {
+        ssl_write_supported_elliptic_curves_ext( ssl, p + 2 + ext_len, &olen );
+        ext_len += olen;
 
-    ssl_write_supported_point_formats_ext( ssl, p + 2 + ext_len, &olen );
-    ext_len += olen;
+        ssl_write_supported_point_formats_ext( ssl, p + 2 + ext_len, &olen );
+        ext_len += olen;
+    }
 #endif
 
 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)