FROMGIT: binder: create node flag to request sender's security context

To allow servers to verify client identity, allow a node
flag to be set that causes the sender's security context
to be delivered with the transaction. The BR_TRANSACTION
command is extended in BR_TRANSACTION_SEC_CTX to
contain a pointer to the security context string.

Signed-off-by: Todd Kjos <tkjos@google.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit ec74136ded792deed80780a2f8baf3521eeb72f9
 https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


 master)
Change-Id: I44496546e2d0dc0022f818a45cd52feb1c1a92cb
Signed-off-by: Todd Kjos <tkjos@google.com>