scsi: target: iscsi: Fix timeout on deleted connection
In the Linux kernel, the following vulnerability has been resolved:

scsi: target: iscsi: Fix timeout on deleted connection

NOPIN response timer may expire on a deleted connection and crash with
such logs:

Did not receive response to NOPIN on CID: 0, failing connection for I_T Nexus (null),i,0x00023d000125,iqn.2017-01.com.iscsi.target,t,0x3d

BUG: Kernel NULL pointer dereference on read at 0x00000000
NIP  strlcpy+0x8/0xb0
LR iscsit_fill_cxn_timeout_err_stats+0x5c/0xc0 [iscsi_target_mod]
Call Trace:
 iscsit_handle_nopin_response_timeout+0xfc/0x120 [iscsi_target_mod]
 call_timer_fn+0x58/0x1f0
 run_timer_softirq+0x740/0x860
 __do_softirq+0x16c/0x420
 irq_exit+0x188/0x1c0
 timer_interrupt+0x184/0x410

That is because nopin response timer may be re-started on nopin timer
expiration.

Stop nopin timer before stopping the nopin response timer to be sure
that no one of them will be re-started.