Clean up RX dissector.

Clean up RX dissector.

Use uintN_t and intN_t types rather than u_short and u_int.

Use uint32_t rather than unsigned long, as that's what's intended.

Most fields in RX are unsigned, according to the OpenAFS source; make it
so.  Use EXTRACT_BE_INT32() to extract the one field that isn't.

The length and port numbers passed in from the UDP dissector are
unsigned; make the arguments unsigned.

Use ND_TTEST2 rather than a hand-rolled test.

Use ND_TCHECK_nBITS() rather than ND_TCHECK2() in some cases.