workspace: update linux to 6.12.15

Switch to the current 6.12 LTS branch and rebase the patches.
Also switch to using savedefconfig for config instead of just including
the entire thing. This makes it much more readable as it only contains
settings we've touched.

Change-Id: I2b15944f0083399290a2539c42e37205e839bf36
Reviewed-on: https://review.monogon.dev/c/monogon/+/3908
Tested-by: Jenkins CI
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
diff --git a/build/bazel/third_party.MODULE.bazel b/build/bazel/third_party.MODULE.bazel
index cf7db66..fa7c757 100644
--- a/build/bazel/third_party.MODULE.bazel
+++ b/build/bazel/third_party.MODULE.bazel
@@ -113,12 +113,12 @@
     urls = ["https://github.com/monogon-dev/gperf/archive/%s.tar.gz" % GPERF_VERSION],
 )
 
-LINUX_VERSION = "6.6.71"
+LINUX_VERSION = "6.12.15"
 
 http_archive(
     name = "linux",
     build_file = "//third_party/linux:linux.bzl",
-    integrity = "sha256-IZcVui3PplOfugmtP5ISdy81Bxietg13+OibBsMuck4=",
+    integrity = "sha256-X/W9hOoOIsU0NzAttdOU0Kkti4saiM4g0QmCmOn3Ywo=",
     patch_args = ["-p1"],
     patches = [
         "//third_party/linux/patches:0001-block-partition-expose-PARTUUID-through-uevent.patch",