A new function "get_linux_version()" to normalize and print the
kernel version as an integer. In some migration scripts, it is
useful for checking the Linux kernel version.
Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/19172
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>