Add argument to tprint_iov() specifying whether to decode each iovec

* defs.h (tprint_iov): Add decode_iov argument.
* io.c (tprint_iov): Implement new decode_iov argument.
(sys_readv, sys_writev, sys_sendfile, sys_preadv, sys_pwritev): Update
tprint_iov calls.
* net.c (do_msghdr): Likewise.
diff --git a/defs.h b/defs.h
index 2c08635..7ffc3f4 100644
--- a/defs.h
+++ b/defs.h
@@ -584,7 +584,7 @@
 extern void printtrailer(void);
 extern void tabto(int);
 extern void call_summary(FILE *);
-extern void tprint_iov(struct tcb *, unsigned long, unsigned long);
+extern void tprint_iov(struct tcb *, unsigned long, unsigned long, int decode_iov);
 extern void tprint_open_modes(mode_t);
 extern const char *sprint_open_modes(mode_t);
 extern int is_restart_error(struct tcb *);