[PATCH] WCCPv2 documentation and cleanup for bug 2404

This patch:
  - adds a reference to each struct mentioning the exact draft
    RFC section where that struct is defined.
  - fixes sent mask structure fields to match draft. (bug 2404)
  - removes two duplicate useless structs

Submitting as a patch to give anyone interested time to double-check the
code changes.

As a result we are a step closer toward splitting the code into a
separate library. It's highlighted some of the WCCPv2 issues and a
pathway forward now clear:
  - move types definitions to a protocol types header (wccp2_types.h ?)
  - correct mangled definitions for generic use. including code in that.
  - add capability handling
  - add hash/mask service negotiation
  - add sibling peer discovery through WCCP group details ??

Amos

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