network: add __network_path_append_bss

To reduce code duplication and prepare for moving the BSS interface
to station, add a new API so station can create a BSS path without
a network object directly.

src/network.c

@@ -1130,17 +1130,23 @@ bool network_update_known_frequencies(struct network *network)
 	return true;
 }
 
-const char *network_bss_get_path(const struct network *network,
-						const struct scan_bss *bss)
+const char *__network_path_append_bss(const char *network_path,
+					const struct scan_bss *bss)
 {
 	static char path[256];
 
 	snprintf(path, sizeof(path), "%s/%02x%02x%02x%02x%02x%02x",
-			network->object_path, MAC_STR(bss->addr));
+			network_path, MAC_STR(bss->addr));
 
 	return path;
 }
 
+const char *network_bss_get_path(const struct network *network,
+						const struct scan_bss *bss)
+{
+	return __network_path_append_bss(network->object_path, bss);
+}
+
 static bool network_unregister_bss(void *a, void *user_data)
 {
 	struct scan_bss *bss = a;

src/network.h

@@ -77,6 +77,9 @@ const char *network_bss_get_path(const struct network *network,
 						const struct scan_bss *bss);
 bool network_bss_list_isempty(struct network *network);
 
+const char *__network_path_append_bss(const char *network_path,
+					const struct scan_bss *bss);
+
 struct scan_bss *network_bss_list_pop(struct network *network);
 struct scan_bss *network_bss_find_by_addr(struct network *network,
 							const uint8_t *addr);