package/mdadm: bump to version 4.6

Drop upstreamed/backported patches.

Release announcements:
4.6: https://lore.kernel.org/linux-raid/CALTww2_2pjjOSsVj-WT++m35555CjnPWokU7fut+HwUJVV-=ZQ@mail.gmail.com/
4.5: https://lore.kernel.org/linux-raid/CALTww293wnLE2+eZsZ42oyNZhS_cc2agB4GNqTz8j3xiP0ALWA@mail.gmail.com/
4.4: https://lore.kernel.org/linux-raid/20241213121438.7ed6a0fd@mtkaczyk-private-dev/

Upstream mdadm project has moved its primary development to GitHub:
https://github.com/md-raid-utilities/mdadm
Updated download site accordingly. See:
https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/commit/README.md?id=3f90be087fa62c0c7ed76c2ac26752f0ac3a89e7

mdadm >= 4.5 removed fallback definitions for MD_DISK_FAILFAST
(commit f5889f9a1b8753a1472dfef9d025da2bae395239), relying on
kernel headers instead.This breaks builds with toolchains using older headers
(e.g. 4.9). So, enforce BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_10.

Since mdadm 4.6, `mdadm --create` may prompt for bitmap configuration,
which breaks the runtime test.Fix the test by passing `--bitmap=none`
to keep it non-interactive.

Signed-off-by: Maxin John <maxin.john@gmail.com>
[Julien:
 - add comment in Config.in
 - add link to upstream commit for repository change in commit log
]
Signed-off-by: Julien Olivain <ju.o@free.fr>

support/testing/tests/package/test_mdadm.py

@@ -69,7 +69,7 @@ class TestMdadm(infra.basetest.BRTest):
         self.assertRunOk(cat_mdstat_cmd)
 
         # We create a raid5 array with the drives.
-        cmd = f"mdadm --create --verbose {md_dev} --level=5 "
+        cmd = f"mdadm --create --verbose {md_dev} --level=5 --bitmap=none "
         cmd += f"--raid-devices={len(storage_devs)} "
         cmd += " ".join(storage_devs)
         self.assertRunOk(cmd)