Use rb_block_call() instead of the deprecated rb_iterate() in OpenSSL

* See https://bugs.ruby-lang.org/issues/18025
  and ruby/ruby#4629

This is a backport to the 2.1 branch.

(cherry picked from commit b8e4852)

ext/openssl/ossl_ssl.c

@@ -33,7 +33,7 @@ static VALUE eSSLErrorWaitReadable;
 static VALUE eSSLErrorWaitWritable;
 
 static ID id_call, ID_callback_state, id_tmp_dh_callback, id_tmp_ecdh_callback,
- id_npn_protocols_encoded;
+ id_npn_protocols_encoded, id_each;
 static VALUE sym_exception, sym_wait_readable, sym_wait_writable;
 
 static ID id_i_cert_store, id_i_ca_file, id_i_ca_path, id_i_verify_mode,
@@ -614,7 +614,7 @@ static VALUE
 ssl_encode_npn_protocols(VALUE protocols)
 {
  VALUE encoded = rb_str_new(NULL, 0);
- rb_iterate(rb_each, protocols, ssl_npn_encode_protocol_i, encoded);
+ rb_block_call(protocols, id_each, 0, 0, ssl_npn_encode_protocol_i, encoded);
  return encoded;
 }
 
@@ -2957,6 +2957,7 @@ Init_ossl_ssl(void)
  id_tmp_dh_callback = rb_intern("tmp_dh_callback");
  id_tmp_ecdh_callback = rb_intern("tmp_ecdh_callback");
  id_npn_protocols_encoded = rb_intern("npn_protocols_encoded");
+ id_each = rb_intern_const("each");
 
 #define DefIVarID(name) do \
  id_i_##name = rb_intern("@"#name); while (0)