Reorder and reorganize header files

Let the includes in the following order:

< system headers >
< libkmod >
< tool >
< local headers >
diff --git a/tools/log.c b/tools/log.c
index 05f6b77..05ff96f 100644
--- a/tools/log.c
+++ b/tools/log.c
@@ -22,7 +22,8 @@
 #include <stdlib.h>
 #include <syslog.h>
 
-#include "libkmod.h"
+#include <libkmod.h>
+
 #include "kmod.h"
 
 static bool log_use_syslog;