Move include guard to the top

Having explicit include above the douible-include guard defines is
potential source for hard to track bugs. Let's move it inside the guard
statement.

Change-Id: I5114a63ce00b03c8eed23565d52969250bd505cc
Related: OS#1539
diff --git a/src/gsm_rlcmac.h b/src/gsm_rlcmac.h
index 8f4039c..2ad1937 100644
--- a/src/gsm_rlcmac.h
+++ b/src/gsm_rlcmac.h
@@ -29,11 +29,12 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  */
 
+#ifndef __PACKET_GSM_RLCMAC_H__
+#define __PACKET_GSM_RLCMAC_H__
+
 #include "csn1.h"
 #include <iostream>
 #include <cstdlib>
-#ifndef __PACKET_GSM_RLCMAC_H__
-#define __PACKET_GSM_RLCMAC_H__
 
 #ifndef PRE_PACKED
 #define PRE_PACKED