fetch: pass --ipv4 and --ipv6 options to sub-fetches

The options indicate user intent for the whole fetch operation, and
ignoring them in sub-fetches (i.e. "--all" and recursive fetching of
submodules) is quite unexpected when, for instance, it is intended
to limit all of the communication to a specific transport protocol
for some reason.

Signed-off-by: Alex Riesen <alexander.riesen@cetitec.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -1531,6 +1531,10 @@ static void add_options_to_argv(struct argv_array *argv)
 		argv_array_push(argv, "-v");
 	else if (verbosity < 0)
 		argv_array_push(argv, "-q");
+	if (family == TRANSPORT_FAMILY_IPV4)
+		argv_array_push(argv, "--ipv4");
+	else if (family == TRANSPORT_FAMILY_IPV6)
+		argv_array_push(argv, "--ipv6");
 
 }