[x86] Tweak kernel version selection

[ashthespy]

From a2efe8bf5e7da00eb639ec8105168f09d01ebd16, isn't https://github.com/volumio/Build/blob/a2efe8bf5e7da00eb639ec8105168f09d01ebd16/recipes/devices/families/x86.sh#L169-L170 a rather roundabout way of just setting the current kernel to vmlinuz? i.e KRNL=vmlinuz

The initial stuff was written to handle multiple kernels - on my system,

lrwxrwxrwx 1 root root       24 jul 29  2020 /boot/vmlinuz -> vmlinuz-5.3.0-64-generic
-rw------- 1 root root 11412224 jun  3  2020 /boot/vmlinuz-5.3.0-59-generic
-rw------- 1 root root 11416320 jun 23  2020 /boot/vmlinuz-5.3.0-62-generic
-rw------- 1 root root 11416320 jul 10  2020 /boot/vmlinuz-5.3.0-64-generic
lrwxrwxrwx 1 root root       24 jul 29  2020 /boot/vmlinuz.old -> vmlinuz-5.3.0-62-generic

This gives:

mapfile -t KRNL_VERS < <(ls -t /boot/vmlinuz-* | sort)
log "Found ${#KRNL_VERS[@]} kernel(s)" "${KRNL_VERS[*]}"
KRNL=${KRNL_VERS[0]##*/}
IFS=- read -ra KVER <<<"$KRNL"
log "KRNL: ${KRNL}"
log "KVER[${#KVER[@]}]:  ${KVER[*]}"

[ .. ] Found 3 kernel(s) [ /boot/vmlinuz-5.3.0-59-generic /boot/vmlinuz-5.3.0-62-generic /boot/vmlinuz-5.3.0-64-generic ]
[ .. ] KRNL: vmlinuz-5.3.0-59-generic 
[ .. ] KVER[4]:  vmlinuz 5.3.0 59 generic 
[ o.k. ] Finished Kernel 5.3.0 installation  [ vmlinuz-5.3.0-59-generic ]

-- so KRNL_VERS was an array of the different kernels found, and KRNL would then pick the most recent version. KVER is then an array built by splitting $KRNL on -

But the current code is a bit of a mix b/w handling multiple kernels, and single ones and thus

mv ${KRNL_VERS[@]} /boot/${KRNL}
# would expand to 
mv /boot/vmlinuz-5.3.0-59-generic /boot/vmlinuz-5.3.0-62-generic /boot/vmlinuz-5.3.0-64-generic /boot/vmlinuz

However, all this is probably moot as I believe we would only have a single Kernel in /boot (especially during image building time) so I simplified it to explicitly set it directly to vmlinuz to avoid any confusion.

[volumio]

Is it tested and safe to merge?

[ashthespy]

Yep, but better @gkkpch reviews it, as this is an extension of a2efe8b..