f2fs: fix to do sanity check on node footer in {read,write}_end_io

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to do sanity check on node footer in {read,write}_end_io

-----------[ cut here ]------------
kernel BUG at fs/f2fs/data.c:358!
Call Trace:
<IRQ>
blk_update_request+0x5eb/0xe70 block/blk-mq.c:987
blk_mq_end_request+0x3e/0x70 block/blk-mq.c:1149
blk_complete_reqs block/blk-mq.c:1224 [inline]
blk_done_softirq+0x107/0x160 block/blk-mq.c:1229
handle_softirqs+0x283/0x870 kernel/softirq.c:579
__do_softirq kernel/softirq.c:613 [inline]
invoke_softirq kernel/softirq.c:453 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1050
</IRQ>

In f2fs_write_end_io(), it detects there is inconsistency in between
node page index (nid) and footer.nid of node page.

If footer of node page is corrupted in fuzzed image, then we load corrupted
node page w/ async method, e.g. f2fs_ra_node_pages() or f2fs_ra_node_page(),
in where we won't do sanity check on node footer, once node page becomes
dirty, we will encounter this bug after node page writeback.