fetch: pass --no-write-fetch-head to subprocesses

It seems a user would expect this option would work regardless
of whether it's fetching from a single remote, many remotes,
or recursing into submodules.

Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -1880,6 +1880,8 @@ static void add_options_to_argv(struct strvec *argv)
 		strvec_push(argv, "--ipv4");
 	else if (family == TRANSPORT_FAMILY_IPV6)
 		strvec_push(argv, "--ipv6");
+	if (!write_fetch_head)
+		strvec_push(argv, "--no-write-fetch-head");
 }
 
 /* Fetch multiple remotes in parallel */