Fix compilation issues on OS X - mainly #include file changes (Lars Immisch)

diff --git a/src/gsm_utils.c b/src/gsm_utils.c
index b0594ae..0c25b28 100644
--- a/src/gsm_utils.c
+++ b/src/gsm_utils.c
@@ -22,7 +22,7 @@
  */
 
 #include <openbsc/gsm_utils.h>
-#include <malloc.h>
+#include <stdlib.h>
 #include <string.h>
 
 /* GSM 03.38 6.2.1 Charachter packing */