NFS: Automounted filesystems should inherit ro,noexec,nodev,sync flags

[ Upstream commit 8675c69816e4276b979ff475ee5fac4688f80125 ]

When a filesystem is being automounted, it needs to preserve the
user-set superblock mount options, such as the "ro" flag.

BUG=b/473763359
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2025-68764 in the Linux kernel.

cos-patch: security-moderate

Reported-by: Li Lingfeng <lilingfeng3@huawei.com>
Link: https://lore.kernel.org/all/20240604112636.236517-3-lilingfeng@huaweicloud.com/
Fixes: f2aedb713c28 ("NFS: Add fs_context support.")
Change-Id: I14e8771beeea47f3055d42d623ac3da608590435
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/124382
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Daniel Velasquez <rdvelasquez@google.com>