Doc: Fix RIP example

<p><code>

protocol rip {

        debug all;

	import all;

	export all;

	interface "eth*" {

		metric 2;

		port 1520;

        period 12;

        garbage time 60;

        interface "eth0" { metric 3; mode multicast; };

        interface "eth*" { metric 2; mode broadcast; };

		mode multicast;

		update time 12;

		timeout time 60;

		authentication cryptographic;

        password "secret-shared-key" { algorithm hmac sha256; };

        import filter { print "importing"; accept; };

        export filter { print "exporting"; accept; };

		password "secret" { algorithm hmac sha256; };

	};

}

</code>