ossl_ssl.c: suppress warnings

* ext/openssl/ossl_ssl.c (ossl_sslctx_setup): fix argument types
  to suppress shorten-64-to-32 and shorten-64-to-32 warnings.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51351 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/openssl/ossl_ssl.c

@@ -869,7 +869,7 @@ ossl_sslctx_setup(VALUE self)
     val = rb_iv_get(self, "@alpn_protocols");
     if (!NIL_P(val)) {
 	VALUE rprotos = ssl_encode_npn_protocols(val);
-	SSL_CTX_set_alpn_protos(ctx, StringValueCStr(rprotos), RSTRING_LEN(rprotos));
+	SSL_CTX_set_alpn_protos(ctx, (const unsigned char *)StringValueCStr(rprotos), RSTRING_LENINT(rprotos));
 	OSSL_Debug("SSL ALPN values added");
     }
     if (RTEST(rb_iv_get(self, "@alpn_select_cb"))) {