In some cases, recent builds fail to boot from flash with at least some
MT7621 based devices. The error message is:
"LZMA ERROR 1 - must RESET board to recover"
Booting the same kernel via TFTP works for some reason.
Through testing I figured out that limiting the LZMA dictionary size
seems to prevent these errors
Signed-off-by: Felix Fietkau <nbd@nbd.name>