scsi: target: core: Fix target_cmd_counter leak

scsi: target: core: Fix target_cmd_counter leak

The target_cmd_counter struct allocated via target_alloc_cmd_counter() is
never freed, resulting in leaks across various transport types, e.g.:

 unreferenced object 0xffff88801f920120 (size 96):
  comm "sh", pid 102, jiffies 4294892535 (age 713.412s)
  hex dump (first 32 bytes):
    07 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 38 01 92 1f 80 88 ff ff  ........8.......
  backtrace:
    [<00000000e58a6252>] kmalloc_trace+0x11/0x20
    [<0000000043af4b2f>] target_alloc_cmd_counter+0x17/0x90 [target_core_mod]
    [<000000007da2dfa7>] target_setup_session+0x2d/0x140 [target_core_mod]
    [<0000000068feef86>] tcm_loop_tpg_nexus_store+0x19b/0x350 [tcm_loop]
    [<000000006a80e021>] configfs_write_iter+0xb1/0x120
    [<00000000e9f4d860>] vfs_write+0x2e4/0x3c0
    [<000000008143433b>] ksys_write+0x80/0xb0
    [<00000000a7df29b2>] do_syscall_64+0x42/0x90
    [<0000000053f45fb8>] entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Free the structure alongside the corresponding iscsit_conn / se_sess
parent.

Signed-off-by: David Disseldorp <ddiss@suse.de>
Link: https://lore.kernel.org/r/20230831183459.6938-1-ddiss@suse.de
Fixes: becd9be6069e ("scsi: target: Move sess cmd counter to new struct")
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>