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/gprs_rlc.c b/src/gprs_rlc.c
index 7ea5437..9e3bed0 100644
--- a/src/gprs_rlc.c
+++ b/src/gprs_rlc.c
@@ -1,6 +1,6 @@
 #include <osmocom/core/utils.h>
 
-#include "gprs_rlc.h"
+#include "protocol/diag_log_gprs_rlc.h"
 
 struct value_string gprs_rlc_ul_state_vals[8] = {
 	{ US_NULL,		"US_NULL" },