it's simple as it is...
I'm using 4.4 with trunk. Just copy patches-4.4 and config-4.4 from 17.01 and change the Makefile to use 4.4.
by @neheb
makefile is under ./target/linux/ramips/makefile
you have to change the 4.9 to 4.4
and copy the patches-4.4 dir to ./target/linux/ramips and config-4.4 file to ./target/linux/ramips/mt7621