kernel: bump 6.12 to 6.12.28

kernel: bump 6.12 to 6.12.28

Changelog: https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.12.28

Removed upstreamed:
        generic/pending-6.12/691-net-ipv6-fix-UDPv6-GSO-segmentation-with-NAT.patch[1]

Manually rebased:
        generic/pending-6.12/737-net-ethernet-mtk_eth_soc-add-paths-and-SerDes-modes-.patch[2]
        generic/hack-6.12/781-usb-net-rndis-support-asr.patch[3]

1. https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-6.12.y&id=6effe1c0fa823d9923f3b77547f201a5bab6c1e5
2. https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-6.12.y&id=aea3ca60fafbdf0da5c930ff2f4105587deb6753
3. https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-6.12.y&id=222b6685efe0d8c1cdb078a67bbe806f56d18f94

All other patches automatically rebased.

Build system: x86/64
Build-tested: x86/64
Run-tested: x86/64

Signed-off-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>
Link: https://github.com/openwrt/openwrt/pull/18756
Signed-off-by: Robert Marko <robimarko@gmail.com>