f2fs: protect extension_list reading with sb_lock in f2fs_sbi_show()

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

f2fs: protect extension_list reading with sb_lock in f2fs_sbi_show()

In f2fs_sbi_show(), the extension_list, extension_count and

hot_ext_count are read without holding sbi->sb_lock. If a concurrent

sysfs store modifies the extension list via f2fs_update_extension_list(),

the show path may read inconsistent count and array contents, potentially

leading to out-of-bounds access or displaying stale data.

Fix this by holding sb_lock around the entire extension list read

and format operation.