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_gsm.c b/src/diag_gsm.c
index d74dc5d..a2d0ea4 100644
--- a/src/diag_gsm.c
+++ b/src/diag_gsm.c
@@ -1,9 +1,9 @@
 #include <osmocom/core/utils.h>
 #include <osmocom/core/msgb.h>
 
-#include "diagcmd.h"
-#include "diag_gsm.h"
-#include "protocol.h"
+#include "protocol/diagcmd.h"
+#include "protocol/diag_log_gsm.h"
+#include "protocol/protocol.h"
 
 const struct value_string diag_gsm_rr_st_vals[] = {
 	{ DIAG_RR_ST_INACTIVE,		"INACTIVE" },