Suggest non-gki kernel users to backport path_umount

[backslashxx]

Most kernel builders have to touch their kernel source code anyway, why not also tell them to backport path_umount so even non-gki users can benefit from this?

I know this might be a bit controversial as this will raise the barrier of entry, but the benefits are just so high.

Idea was from OnlyTomInSecond on KernelSU group chat way back, and it has been on the discussions for some time

references: https://t.me/KernelSU_group/27237/176515 https://t.me/KernelSU_group/3249/184908 https://github.com/tiann/KernelSU/discussions/955#discussioncomment-7617166 https://github.com/OnlyTomInSecond/android_kernel_xiaomi_sdm845/commit/03d233db8bbe9fe101509430bfa09d1899168aa7 https://github.com/tiann/KernelSU/pull/1060

https://elixir.bootlin.com/linux/v5.9.1/source/fs/namespace.c#L1728 https://elixir.bootlin.com/linux/v5.10.9/source/fs/namespace.c#L1730 https://elixir.bootlin.com/linux/v6.8.1/source/fs/namespace.c#L1889 https://github.com/tiann/KernelSU/pull/1464#issuecomment-2002492107

Kernel side change examples 5.4 https://github.com/natsumerinchan/kernel_oneplus_sm8350/commit/961d9788624e88c3c58918b3781b9fbdd19ecbeb 4.19 https://github.com/backslashxx/android_karnol_ximi_fog/commit/164917f56d0e75ab51bb9f1bdf489acac7a6d3db 4.14 https://github.com/backslashxx/mojito_krenol/commit/686e90b6a63ad0851e964bddab7add54ec52b973 4.9 https://github.com/backslashxx/msm8953-los21/commit/195f07593ae9769a992f3945bcdc43ff7fc99827 4.4 https://github.com/riarumoda/android_kernel_samsung_a9y18qlte/commit/21ea33fe41ce079ec1d663c0bd2201bc00a8084a https://github.com/tiann/KernelSU/pull/1464#issuecomment-2002424069 ofcourse having someone on 3.18 confirm this will be nice.

PROS: umount modules for everyone CONS: barrier of entry +1