mboxd: Refactor and rename mbox.h to mboxd.h

Refine the purpose of the header file to represent what's required for
the daemon itself, not its constituent pieces. Rather, split those
definitions out to their respective header files and include them as
necessary.

Finally the header file is renamed to better reflect its purpose.

Change-Id: I48c409f57d96c844589cd865b24f197477dfe87c
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/protocol_negotiate_version.c b/protocol_negotiate_version.c
index 849363f..16b8e64 100644
--- a/protocol_negotiate_version.c
+++ b/protocol_negotiate_version.c
@@ -4,7 +4,7 @@
 
 #include <errno.h>
 
-#include "mbox.h"
+#include "mboxd.h"
 #include "protocol.h"
 
 static const struct protocol_ops protocol_ops_v1 = {