lib: fix strutils.h, remove STRTOXX_EXIT_CODE

As discussed on the mailing list. We fix all places
where the non-working define STRTOXX_EXIT_CODE was used.

Regarding tunelp, also see 7e3c80a7.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>

include/strutils.h

@@ -9,11 +9,8 @@
 #include <stdio.h>
 #include <errno.h>
 
-/* default strtoxx_or_err() exit code */
-#ifndef STRTOXX_EXIT_CODE
-# define STRTOXX_EXIT_CODE EXIT_FAILURE
-#endif
-
+/* initialize a custom exit code for all *_or_err functions */
+extern void strutils_set_exitcode(int exit_code);
 
 extern int parse_size(const char *str, uintmax_t *res, int *power);
 extern int strtosize(const char *str, uintmax_t *res);