blockcheck: enable tls-max with LibreSSL based curl

blockcheck.sh

@@ -267,8 +267,8 @@ curl_supports_tls13()
 }
 curl_supports_tlsmax()
 {
-	# supported only in OpenSSL
-	curl --version | grep -Fq OpenSSL || return 1
+	# supported only in OpenSSL and LibreSSL
+	curl --version | grep -Fq -e OpenSSL -e LibreSSL || return 1
 	# supported since curl 7.54
 	curl --tls-max 1.2 -Is -o /dev/null http://$LOCALHOST_IPT:65535 2>/dev/null
 	# return code 2 = init failed. likely bad command line options