GitLab

This resolves skiboot failing to receive the mboxd termination message
if mboxd has been killed unexpectedly or due to some race on shutdown
where the message fails to propagate.

Change-Id: I7a0974fc17f6853ac62c1f5f7b43d2e367260cf6
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>