Tvbuffify the RIP and OSPF dissectors.

Tvbuffify the RIP and OSPF dissectors.

Change them to use facilities in Ethereal that were probably not present
when they were originally written, e.g. routines to fetch 24-bit
integers and to dump a bunch of raw bytes in hex.

Redo them to extract data from the packet as they dissect it, rather
than extracting an entire data structure at once; that way, it may be
able to dissect a structure not all of which is in the packet.

Dissect a bit more of the type-of-service metrics etc. in OSPF packets.

Make "tvb_length_remaining()" return a "gint", not a "guint"; it returns
-1 if the offset is past the end of the tvbuff.

Add a "tvb_reported_length_remaining()" routine, similar to
"tvb_length_remaining()".  Use it instead of just subtracting an offset
from "tvb_reported_length()".

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@2787 f5534014-38df-0310-8fa8-9805f1628bb7