cmd/snap-confine: use SNAP_MOUNT_DIR to setup /snap inside the confinement env

cmd/snap-confine/mount-support.c

@@ -641,8 +641,10 @@ static bool is_mounted_with_shared_option(const char *dir)
 void sc_ensure_shared_snap_mount()
 {
 	if (!is_mounted_with_shared_option("/")
-	    && !is_mounted_with_shared_option("/snap")) {
-		sc_do_mount("/snap", "/snap", "none", MS_BIND | MS_REC, 0);
-		sc_do_mount("none", "/snap", NULL, MS_SHARED | MS_REC, NULL);
+	    && !is_mounted_with_shared_option(SNAP_MOUNT_DIR)) {
+		sc_do_mount(SNAP_MOUNT_DIR, SNAP_MOUNT_DIR, "none",
+			    MS_BIND | MS_REC, 0);
+		sc_do_mount("none", SNAP_MOUNT_DIR, NULL, MS_SHARED | MS_REC,
+			    NULL);
 	}
 }