package: basefiles: add oem image dectection to fwtool.sh

package: basefiles: add oem image dectection to fwtool.sh

with more new device, now able to flash oem
images from luci, fwtools erroneously marks
firmware as incompatible and does not warn
across keeping configs during update.

this patch aims to add both oem detection
and a warning msg advising firmware is compatible
(OpenWrt -> OEM) but configuration is not

tested on ipq5018: gl-b3000

Signed-off-by: Scott Mercer <TheRootEd24@gmail.com>
package: basefiles: add oem image dectection to fwtool

    some new devices are now able to flash oem
    images from luci, fwtools erroneously marks
    firmware as incompatible and does not warn
    of keeping configs during update for this condition.

    this patch aims to add both oem detection
    and trigger the existing warning msg, advising firmware is compatible
    (OpenWrt -> OEM) but configuration is not

tested on ipq5018: gl-b3000

Signed-off-by: Scott Mercer <TheRootEd24@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/18554
Signed-off-by: Robert Marko <robimarko@gmail.com>