submodule-config: keep shallow recommendation around

The shallow field will be used in a later patch by `submodule update`.
To differentiate between the actual depth (which may be different),
we name it `recommend_shallow` as the field in the .gitmodules file
is only a recommendation by the project.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

submodule-config.h

@@ -18,6 +18,7 @@ struct submodule {
 	struct submodule_update_strategy update_strategy;
 	/* the sha1 blob id of the responsible .gitmodules file */
 	unsigned char gitmodules_sha1[20];
+	int recommend_shallow;
 };
 
 int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);