target: Support aborting tasks with a 64-bit tag

Avoid truncating the tag argument of target_submit_tmr() to a
32-bit number if the caller passes a 64-bit number.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>