zfs: add bounds checking to zil_parse (#16308)

Make sure log record don't stray beyond valid memory region.

There is a lack of verification of the space occupied by fixed members
of lr_t in the zil_parse.

We can create a crafted image to trigger an out of bounds read by
following these steps:

1. Do some file operations and reboot to simulate abnormal exit without umount
2. zil_chain.zc_nused: 0x1000
3. First lr_t lr_t.lrc_txtype: 0x0 lr_t.lrc_reclen: 0x1000-0xb8-0x1 lr_t.lrc_txg: 0x0 lr_t.lrc_seq: 0x1
4. Update checksum in zil_chain.zc_eck

Fix:
Add some checks to make sure the remaining bytes are large enough to
hold an log record.

Signed-off-by: XDTG <click1799@163.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>