CVE-2025-71123 ext4: fix string copying in parse_apply_sb_mount_options()

In the Linux kernel, the following vulnerability has been resolved: ext4: fix string copying in parseapplysbmountoptions strscpypad can't be used to copy a non-NUL-term string into a NUL-term string of possibly bigger size. Commit 0efc5990bca5 "string.h: Introduce memtostr and memtostrpad" provid...