Allow messages to be sent between all VMs.

Any VM can send a message to any other VM. The hypervisor acts as a
router to deliver the message to the destination but does not track
higher level state about the communications.

When receiving a message, the source VM is reported so access controls
can be applies and replies can be sent back.

Bug: 116705004
Change-Id: Ib83988eb8ddee1753dfd67a3baa3fb991ebd4dd7
diff --git a/src/vm.c b/src/vm.c
index 0958682..b62238d 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -24,7 +24,7 @@
 
 	vm->id = vm_count;
 	vm->vcpu_count = vcpu_count;
-	vm->rpc.state = rpc_state_idle;
+	vm->mailbox.state = mailbox_state_empty;
 
 	/* Do basic initialization of vcpus. */
 	for (i = 0; i < vcpu_count; i++) {