Econet uses custom vendor kernel based on 5.4 from Git. Broadcom uses
"fake" kernel from Git (only used for installing uapi-headers). OpenWrt
22.03 introduced a sanity check whether the hashes exists, even when
using a kernel from Git, so these hashes for tarballs are irrelevant.

Signed-off-by: Andreas Gnau <andreas.gnau@iopsys.eu>