openssh-7.1: Set path for xauth

Currently the warning below is shown, logging in over SSH.

```
> ssh deinemuddah
Warning: No xauth data; using fake authentication data for X11 forwarding.
```

As a result, forwarding X programs does not work anymore.

```
> xclock
Error: Can't open display:
```

The problem is, that the xauth binary is hard-coded into the SSHD binary
during build time, and set to `/usr/X11R6/bin/xauth`.

```
> strings /usr/sbin/sshd | grep X11R
/usr/X11R6/bin/xauth
```

So manually set it to `/usr/bin/xauth`, as this is where it’s stored in
Mariux.

Debian does the same [1].

[1] https://anonscm.debian.org/cgit/pkg-ssh/openssh.git/tree/debian/rules#99

openssh-7.1_p2-0.bee

@@ -11,7 +11,8 @@ mee_configure() {
         --sysconfdir=${SYSCONFDIR} \
         --with-md5-passwords \
         --with-privsep-path=/var/lib/sshd \
-        --with-pam
+        --with-pam \
+        --with-xauth=/usr/bin/xauth
 }
 
 mee_install_post() {