Tweak RXGK error code descriptions

Do not restrict BAD{LEVEL,ETYPE} to the negotiation RPCs.

Change-Id: I9b581d31d342907cb6fdfbf3902a1c49137d3283
Mention non-database non-files AFS servers

E.g., bosserver, which must run a negotiation service for the
bootstrapping stage.

Change-Id: I83bb749310bf030c1f342a31d1e0e0217e249946
Allow empty authenticator appdata opaque for bosserver

We don't need a cache manager to talk to a bosserver (or potentially
other non-db, non-fileservers) and may not have a stable UUID available.

Change-Id: I28b62bf5f711066b8f43e2680d4abffa949b99cd
Prescribe leap of faith for RegisterAddrsAndKey

Bind a GSSAPI identity to fileserver UUID, needed to authenticate
future operations on that database entry.  Also suggest periodic
rekeying per best practice on key lifetimes.

Change-Id: Idec26ee2184fd458186fcbdc4783dbea7d29b4eb
Inline VL_RegisterAddrs elements

Do not attempt to incorporate by reference a reference which does
not exist.

Change-Id: I41d725a7ef27525be2002919d04980a45d89c289