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/net.c b/net.c
index 0d8e22d..c9c1847 100644
--- a/net.c
+++ b/net.c
@@ -1409,7 +1409,7 @@
 
 	tprintf(", msg_iov(%lu)=", (unsigned long)msg->msg_iovlen);
 	tprint_iov(tcp, (unsigned long)msg->msg_iovlen,
-		   (unsigned long)msg->msg_iov);
+		   (unsigned long)msg->msg_iov, 1);
 
 #ifdef HAVE_STRUCT_MSGHDR_MSG_CONTROL
 	tprintf(", msg_controllen=%lu", (unsigned long)msg->msg_controllen);