toolbox/modprobe: Fix fallback path when mod_dirs is empty

Due to GKI, the kernel UTS release string will not always (if ever)
match the vendor's UTS release string that is used to create the
initramfs file structure -- /lib/modules/<vendor uname>. This causes
module load failures when `-d DIR` is omitted. To fix this, we can
include all of the versions under /lib/modules that match the kernel's
major and minor version instead of directly using the value of uname().
In addition, we can also support modules being loaded directly from
/lib/modules.

Test: verify GKI kernel + initramfs with different UTS strings
Test: verify GKI kernel + initramfs with modules directly in /lib/modules
Fixes: 83207784 ("toolbox/modprobe: Fallback to /lib/modules/<uname> ")
Bug: 282917063
Bug: 254835242
Merged-In: I5368f5cff139ba3165323a6a91066be38bfa0736
Change-Id: I5368f5cff139ba3165323a6a91066be38bfa0736