1) copy target/linux/mvebu/config-4.0 to target/linux/mvebu/config-4.3
2) create target/linux/mvebu/patches-4.3/ directory and populate with patches from here: https://github.com/nitroshift/wrt1900ac-4.3-patches/tree/master/patches-4.3 (courtesy of nitroshift)
3) Update KERNEL_PATCHVER in target/linux/mvebu/Makefile to 4.3
4) make sure you are on trunk as recent panic bug was fixed (https://dev.openwrt.org/changeset/47447)
5) compile the image as you normally would
6) profit
Fuente: https://forum.openwrt.org/viewtopic.php?pid=299544#p299544
