allow going back from workflow selection

include/menu.h

     char *buff;
 };
 
-void menu_init(void (*cb)(int));
+void menu_init(void (*enter)(int), void (*exit)(void));
 void menu_deinit(void);
 
 void menu_run(void (*cb)(struct menu_state *));

src/menu.c

 static char buff[MENU_MAX_LEN] = {0};
 static struct menu_state menu = { .off = 0, .selection = -1, .length = 0, .buff = buff };
 static void (*enter_callback)(int) = NULL;
+static void (*exit_callback)(void) = NULL;
 
 static void menu_buttons(enum buttons btn, bool state) {
     if (state && (btn == BTN_LEFT)) {
             enter_callback(menu.selection);
         }
         return;
+    } else if (state && (btn == BTN_Y)) {
+        if (exit_callback) {
+            exit_callback();
+        }
     } else if ((!state) || ((btn != BTN_UP) && (btn != BTN_DOWN))) {
         return;
     }
     }
 }
 
-void menu_init(void (*cb)(int)) {
+void menu_init(void (*enter)(int), void (*exit)(void)) {
     menu.off = 0;
     menu.selection = -1;
     menu.length = 0;
 
-    enter_callback = cb;
+    enter_callback = enter;
+    exit_callback = exit;
     buttons_callback(menu_buttons);
 }
 

src/state_scan.c

 }
 
 void state_scan_enter(void) {
-    menu_init(enter_cb);
+    menu_init(enter_cb, NULL);
     ble_scan(BLE_SCAN_ON);
 }
 

src/state_volcano_workflow.c

     }
 }
 
+static void exit_cb(void) {
+    state_switch(STATE_SCAN);
+}
+
 void state_volcano_wf_enter(void) {
-    menu_init(enter_cb);
+    menu_init(enter_cb, exit_cb);
 }
 
 void state_volcano_wf_exit(void) {