generic: Convert incorrect generic/5.15 patches again

generic: Convert incorrect generic/5.15 patches again

OpenWrt's developer guide prefers having actual patches so they an be
sent upstream more easily.

However, in the case of hack-5.15 patches which are not meant for
upstream, adding proper fields allows for `git am` to properly function.

This commit tries to rectify that, by digging in the history to find
where and how it was first added.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>