Ignore disabled ciphers when deciding if we are using ECC

use_ecc() was always returning 1 because there are default (TLSv1.3)
ciphersuites that use ECC - even if those ciphersuites are disabled by
other options.

Fixes #7471
Reviewed-by: NKurt Roeckx <kurt@roeckx.be>
(Merged from https://github.com/openssl/openssl/pull/7479)

ssl/statem/extensions_clnt.c

@@ -115,7 +115,7 @@ EXT_RETURN tls_construct_ctos_srp(SSL *s, WPACKET *pkt, unsigned int context,
 #ifndef OPENSSL_NO_EC
 static int use_ecc(SSL *s)
 {
-    int i, end;
+    int i, end, ret = 0;
     unsigned long alg_k, alg_a;
     STACK_OF(SSL_CIPHER) *cipher_stack = NULL;
 
@@ -123,7 +123,7 @@ static int use_ecc(SSL *s)
     if (s->version == SSL3_VERSION)
         return 0;
 
-    cipher_stack = SSL_get_ciphers(s);
+    cipher_stack = SSL_get1_supported_ciphers(s);
     end = sk_SSL_CIPHER_num(cipher_stack);
     for (i = 0; i < end; i++) {
         const SSL_CIPHER *c = sk_SSL_CIPHER_value(cipher_stack, i);
@@ -132,11 +132,14 @@ static int use_ecc(SSL *s)
         alg_a = c->algorithm_auth;
         if ((alg_k & (SSL_kECDHE | SSL_kECDHEPSK))
                 || (alg_a & SSL_aECDSA)
-                || c->min_tls >= TLS1_3_VERSION)
-            return 1;
+                || c->min_tls >= TLS1_3_VERSION) {
+            ret = 1;
+            break;
+        }
     }
 
-    return 0;
+    sk_SSL_CIPHER_free(cipher_stack);
+    return ret;
 }
 
 EXT_RETURN tls_construct_ctos_ec_pt_formats(SSL *s, WPACKET *pkt,