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_gprs.c b/src/diag_log_gprs.c
index f267600..3225d6a 100644
--- a/src/diag_log_gprs.c
+++ b/src/diag_log_gprs.c
@@ -1,10 +1,9 @@
 #include <stdio.h>
 
 #include "diag_log.h"
-#include "diag_gsm.h"
-#include "gprs_rlc.h"
-#include "gprs_mac.h"
-#include "log_codes_gsm.h"
+#include "protocol/diag_log_gsm.h"
+#include "protocol/diag_log_gprs_rlc.h"
+#include "protocol/diag_log_gprs_mac.h"
 
 
 static void handle_grr_state_msg(struct log_hdr *lh, struct msgb *msg)