file capabilities: simplify signal check

Simplify the uid equivalence check in cap_task_kill().  Anyone can kill a
process owned by the same uid.

Without this patch wireshark is reported to fail.

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