Add a enum for decoding to tprint_iov() and tprint_iov_upto()

Introduce a new type iov_decode which will be used instead of the integer
"decode" as a parameter.

* defs.h (iov_decode): New enum.
(tprint_iov, tprint_iov_upto): Change type of "decode_iov" to enum iov_decode.
* aio.c (print_iocb): Change type of "decode_iov" to enum iov_decode in
tprint_iov() call.
* keyctl.c (keyctl_instantiate_key_iov): Likewise.
* process.c (ptrace): Likewise.
* process_vm.c (process_vm_readv, process_vm_writev): Likewise.
* io.c (writev, do_pwritev, vmsplice): Likewise.
(print_iovec): Replace the condition with a switch.
(tprint_iov_upto): Change type of "decode_iov" to enum iov_decode.
(readv, do_preadv): Change type of "decode_iov" to enum iov_decode in
tprint_iov_upto() call.
* scsi.c (print_sg_io_v3_req, print_sg_io_v3_res, print_sg_io_v4_req,
print_sg_io_v4_res): Likewise.
* net.c (do_msghdr): Adapt call of tprint_iov_upto().
diff --git a/scsi.c b/scsi.c
index 83ff8fe..dc51dd5 100644
--- a/scsi.c
+++ b/scsi.c
@@ -84,7 +84,8 @@
 		tprintf(", data[%u]=", sg_io.dxfer_len);
 		if (sg_io.iovec_count)
 			tprint_iov_upto(tcp, sg_io.iovec_count,
-					(unsigned long) sg_io.dxferp, 1,
+					(unsigned long) sg_io.dxferp,
+					IOV_DECODE_STR,
 					sg_io.dxfer_len);
 		else
 			print_sg_io_buffer(tcp, (unsigned long) sg_io.dxferp,
@@ -112,7 +113,8 @@
 		tprintf(", data[%u]=", din_len);
 		if (sg_io.iovec_count)
 			tprint_iov_upto(tcp, sg_io.iovec_count,
-					(unsigned long) sg_io.dxferp, 1,
+					(unsigned long) sg_io.dxferp,
+					IOV_DECODE_STR,
 					din_len);
 		else
 			print_sg_io_buffer(tcp, (unsigned long) sg_io.dxferp,
@@ -163,7 +165,7 @@
 	tprintf(", dout[%u]=", sg_io.dout_xfer_len);
 	if (sg_io.dout_iovec_count)
 		tprint_iov_upto(tcp, sg_io.dout_iovec_count, sg_io.dout_xferp,
-				1, sg_io.dout_xfer_len);
+				IOV_DECODE_STR, sg_io.dout_xfer_len);
 	else
 		print_sg_io_buffer(tcp, sg_io.dout_xferp, sg_io.dout_xfer_len);
 	return 1;
@@ -188,7 +190,7 @@
 	tprintf(", din[%u]=", din_len);
 	if (sg_io.din_iovec_count)
 		tprint_iov_upto(tcp, sg_io.din_iovec_count, sg_io.din_xferp,
-				1, din_len);
+				IOV_DECODE_STR, din_len);
 	else
 		print_sg_io_buffer(tcp, sg_io.din_xferp, din_len);
 	tprintf(", driver_status=%u", sg_io.driver_status);