external/openssh: update to 6.8p1.

In preparation for some updates to external/openssh to make it work with
BoringSSL, this change updates the code to a recent version. The current
version (5.9p1) is coming up on four years old now.

  * Confirmed that f5c67b478bef9992de9e9ec91ce10af4f6205e0d matches
    OpenSSH 5.9p1 exactly (save for the removal of the scard
    subdirectory).

  * Downloaded openssh-6.8p1.tar.gz (SHA256:
    3ff64ce73ee124480b5bf767b9830d7d3c03bbcb6abe716b78f0192c37ce160e)
    and verified with PGP signature. (I've verified Damien's key in
    person previously.)

  * Applied changes between f5c67b478bef9992de9e9ec91ce10af4f6205e0d and
    OpenSSH 5.9p1 to 6.8p1 and updated the build as best I can. The
    ugliest change is probably the duplication of umac.c to umac128.c
    because Android conditionally compiles that file twice. See the
    comment in those files.

Change-Id: I63cb07a8118afb5a377f116087a0882914cea486
diff --git a/ssh-sandbox.h b/ssh-sandbox.h
old mode 100755
new mode 100644
index dfecd5a..bd5fd83
--- a/ssh-sandbox.h
+++ b/ssh-sandbox.h
@@ -15,9 +15,10 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+struct monitor;
 struct ssh_sandbox;
 
-struct ssh_sandbox *ssh_sandbox_init(void);
+struct ssh_sandbox *ssh_sandbox_init(struct monitor *);
 void ssh_sandbox_child(struct ssh_sandbox *);
 void ssh_sandbox_parent_finish(struct ssh_sandbox *);
 void ssh_sandbox_parent_preauth(struct ssh_sandbox *, pid_t);