CVE-2017-13049/Rx: add a missing bounds check for Ubik

One of the case blocks in ubik_print() didn't check bounds before
fetching 32 bits of packet data and could overread past the captured
packet data by that amount.

This fixes a buffer over-read discovered by Henri Salo from Nixu
Corporation.

Add a test using the capture file supplied by the reporter(s).
is_ubik(uint32_t opcode)
{
	if ((opcode >= VOTE_LOW && opcode <= VOTE_HIGH) ||
	    (opcode >= DISK_LOW && opcode <= DISK_HIGH))
		return(1);
	else
		return(0);
}

is_ubik(uint32_t opcode)
{
	if ((opcode >= VOTE_LOW && opcode <= VOTE_HIGH) ||
	    (opcode >= DISK_LOW && opcode <= DISK_HIGH))
		return(1);
	else
		return(0);
}
