A block can have zero or more instances of a given option. We
distinguish between "one instance only" options, where a block can have
zero or one instance, and "multiple instances allowed" options, where a
block can have zero or more instances.
For "one instance only" options:
"add" routines add an instance if there isn't one already
and fail if there is;
"set" routines add an instance if there isn't one already
and change the value of the existing instance if there is one;
"set nth" routines fail;
"get" routines return the value of the instance if there is one
and fail if there isn't;
"get nth" routines fail.
For "multiple instances allowed" options:
"add" routines add an instance;
"set" routines fail;
"set nth" routines set the value of the nth instance if there is
one and fail otherwise;
"get" routines fail;
"get nth" routines get the value if the nth instance if there is
one and fail otherwise.
Rename "optionblock" to just "block"; it describes the contents of a
block, including both mandatory items and options.
Add some support for NRB options, including IPv4 and IPv6 option types.
Change-Id: Iad184f668626c3d1498b2ed00c7f1672e4abf52e
Reviewed-on: https://code.wireshark.org/review/16444
Reviewed-by: Guy Harris <guy@alum.mit.edu>
