security: filesystem capabilities: fix CAP_SETPCAP handling

The filesystem capability support meaning for CAP_SETPCAP is less powerful
than the non-filesystem capability support.  As such, when filesystem
capabilities are configured, we should not permit CAP_SETPCAP to 'enhance'
the current process through strace manipulation of a child process.

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>