modules: update OpenWrt

f8cc68670fcf mediatek: fix parallel build issues in image build code
1086408b17fa mtd: improve check for TRX header being already fixed
5dca299fabc4 mtd: support bad blocks within the mtd_fixtrx()
5889cf70e99f kmod-sched-cake: bump to 20180716
393ee8d0b28a qos-scripts: fix uci callback handling
c9c0fc28a9c4 base-files: fix UCI config parsing and callback handling
aee917a5a28d apm821xx: fix usb-otg on 4.14
3539430b3daa odhcp6c: add noserverunicast config option for broken DHCPv6 servers
6363377c477f odhcp6c: update to latest git HEAD
ce8cab388aab odhcp6c: user string option support
dc52b7b104aa ipq40xx: add get_status_led to diag.sh
7fc7128b086a OpenWrt v18.06.0-rc2: revert to branch defaults
4de335bdbed6 OpenWrt v18.06.0-rc2: adjust config defaults
e4d0ee5af5a0 uhttpd: update to latest Git head