fs,userns: Change inode_capable to capable_wrt_inode_uidgid

fs,userns: Change inode_capable to capable_wrt_inode_uidgid

The kernel has no concept of capabilities with respect to inodes; inodes
exist independently of namespaces.  For example, inode_capable(inode,
CAP_LINUX_IMMUTABLE) would be nonsense.

This patch changes inode_capable to check for uid and gid mappings and
renames it to capable_wrt_inode_uidgid, which should make it more
obvious what it does.

Fixes CVE-2014-4014.

Cc: Theodore Ts'o <[email protected]>
Cc: Serge Hallyn <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: [email protected]
Signed-off-by: Andy Lutomirski <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>