draft-ietf-iptel-trip-mib-04.txt changes

Changes from draft-ietf-iptel-trip-mib-03.txt

- created a separate module, TRIP-TC for the textual conventions

- changed the TC's tripSupportedProtocols and tripAddressFamilies to
integers out of concern that they could very easily be larger than
the 128 subId limit for indexes and to make them much more readable

- removed the tripMIBAdmin subtree since it was not needed to hold
any TC's that are object identifiers

- actually used TripSendReceiveMode

- document is up to date with latest Instructions to Request for
Comments (RFC) Authors - "draft-rfc-editor-rfc2223bis-02.txt"

- cleaned up some descriptions and clarified some persistency
attributes