sys-kernel/coreos-module: use strip-debug instead of strip-unneeded

With `--strip-unneeded` some static symbols are also stripped from modules, making stacktraces
incomplete, and making it harder to debug kernel issues. Switch to the default setting of
`--strip-debug`, which keeps symbols intact and does not appear to lead to a measurable
size increase of the /usr partition.

sys-kernel/coreos-modules/coreos-modules-5.15.70.ebuild

@@ -38,7 +38,7 @@ src_install() {
 	# The linux-firmware package will be used instead.
 	# Stripping must be done here, not portage, to preserve sigs.
 	kmake INSTALL_MOD_PATH="${D}/usr" \
-		  INSTALL_MOD_STRIP="--strip-unneeded" \
+		  INSTALL_MOD_STRIP="--strip-debug" \
 		  INSTALL_FW_PATH="${T}/fw" \
 		  modules_install