iscsi-scstd: Fix redefinition of bool when building with GCC 15

GCC 15 (C23) now reserves bool/true/false, so the local typedef in
iscsid.d breaks the build:

    error: cannot use keyword 'false' as enumeration constant
    error: expected ';', identifier or '(' before 'bool'

Include <stdbool.h> and drop the typedef.

iscsi-scst/usr/iscsid.h

@@ -23,6 +23,7 @@
 #include <assert.h>
 #include <netdb.h>
 #include <syslog.h>
+#include <stdbool.h>
 
 #include "types.h"
 #ifdef INSIDE_KERNEL_TREE
@@ -36,10 +37,6 @@
 #include "param.h"
 #include "misc.h"
 
-#ifndef bool
-typedef enum {false = 0, true} bool;
-#endif
-
 #define sBUG() assert(0)
 #define sBUG_ON(p) assert(!(p))