[PATCH] contrib: fix out-of-tree build with jerry-rig.sh

[Benedikt Morbach]

Hi Jason,

I started doing out-of-tree kernel builds with "make KBUILD_OUTPUT=/foo".
While it does work, it puts wireguards .o files in
/foo/net/../../../..../wireguard/src, which isn't exactly what I
expected/intended. By changing the path in the Makefile the .o files
end up in /foo/net/wireguard.

Thanks
Benedikt