tcmu: Fix some memory corruption

"udev->nl_reply_supported" is an int but on 64 bit arches we are writing
8 bytes of data to it so it corrupts four bytes beyond the end of the
struct.

Fixes: b849b456 ("target: Add netlink command reply supported option for each device")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>