tmpfs: preserve SB_I_VERSION on remount

tmpfs: preserve SB_I_VERSION on remount

Now tmpfs enables i_version by default and tmpfs does not modify it.  But
SB_I_VERSION can also be modified via sb_flags, and reconfigure_super()
always overwrites the existing flags with the latest ones.  This means
that if tmpfs is remounted without specifying iversion, the default
i_version will be unexpectedly disabled.

To ensure iversion remains enabled, SB_I_VERSION is now always set for
fc->sb_flags in shmem_init_fs_context(), instead of for sb->s_flags in
shmem_fill_super().

Link: https://lkml.kernel.org/r/20250819061803.1496443-1-libaokun@huaweicloud.com
Fixes: 36f05cab0a2c ("tmpfs: add support for an i_version counter")
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>