modules: update OpenWrt

3e81365141e4 kernel: gen_stats: Fix netlink stats dumping in the presence of padding
dd1f97b37d41 ramips: clean up and fix MT7621 NAND driver issues
68f40d7ecc4c mt76: update to the latest version
16a9ddfe64e2 ramips: ethernet: use own page_frag_cache
0e6cfb691914 ramips: ethernet: use skb_free_frag to free fragments