core: ivshmem: Notify remote about state change on cell removal

Removing one peer cell has the implicit effect of resetting its state to
0. Signal this change via an interrupt as well.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

hypervisor/ivshmem.c

@@ -309,10 +309,13 @@ static void ivshmem_disconnect_cell(struct ivshmem_data *iv, int cellnum)
 	struct ivshmem_endpoint *remote = &iv->eps[(cellnum + 1) % 2];
 	struct ivshmem_endpoint *ive = &iv->eps[cellnum];
 
+	remote->remote = NULL;
+	memory_barrier();
+	arch_ivshmem_write_doorbell(ive);
+
 	ive->device->ivshmem_endpoint = NULL;
 	ive->device = NULL;
 	ive->remote = NULL;
-	remote->remote = NULL;
 }
 
 /**