Don't fail if the PSK identity doesn't match

In 1.1.0 s_server if the PSK identity doesn't match what we have then
a warning is printed and we continue the connection anyway. In 1.1.1,
if TLSv1.3 is used and the identity doesn't match then we abort the
connection. We should really be consistent with the old behaviour.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6659)

apps/s_server.c

@@ -192,8 +192,11 @@ static int psk_find_session_cb(SSL *ssl, const unsigned char *identity,
     const SSL_CIPHER *cipher = NULL;
 
     if (strlen(psk_identity) != identity_len
-            || memcmp(psk_identity, identity, identity_len) != 0)
-        return 0;
+            || memcmp(psk_identity, identity, identity_len) != 0) {
+        BIO_printf(bio_s_out,
+                   "PSK warning: client identity not what we expected"
+                   " (got '%s' expected '%s')\n", identity, psk_identity);
+    }
 
     if (psksess != NULL) {
         SSL_SESSION_up_ref(psksess);