header file restructuring

Move all protocol definitions to protocol/*.h and keep only
definitions related to our implementation as *.h in the top directory.

Also, remove some header files to reduce header file proliferation.
diff --git a/src/diag_log_qmi.c b/src/diag_log_qmi.c
index b6f7eb5..cc9f0a8 100644
--- a/src/diag_log_qmi.c
+++ b/src/diag_log_qmi.c
@@ -4,7 +4,7 @@
 #include <libqmi-glib.h>
 
 #include "diag_log.h"
-#include "log_codes_qmi.h"
+#include "protocol/diag_log_qmi.h"
 
 /* A small wrapper around libqmi-glib to give us a human-readable string
  * representation of QMI messages that we receive from DIAG */