vfs: create a generic checking and prep function for FS_IOC_SETFLAGS

vfs: create a generic checking and prep function for FS_IOC_SETFLAGS

Create a generic function to check incoming FS_IOC_SETFLAGS flag values
and later prepare the inode for updates so that we can standardize the
implementations that follow ext4's flag values.

Note that the efivarfs implementation no longer fails a no-op SETFLAGS
without CAP_LINUX_IMMUTABLE since that's the behavior in ext*.

Signed-off-by: Darrick J. Wong <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Acked-by: David Sterba <[email protected]>
Reviewed-by: Bob Peterson <[email protected]>