Add handling of large unsigned Integers for ETSILI

[li-guy]

Two special cases in 102 232-3 and 102 232-4 which call for large unsigned Integers

octetsReceived [13] INTEGER (0..18446744073709551615) OPTIONAL,
-- The number of octets the target received
octetsTransmitted [14] INTEGER (0..18446744073709551615) OPTIONAL,
-- The number of octets the target transmitted

[salcock]

Those upper limits are dumb.

A signed 64 bit integer would get you 9223372036854775807 as a max value, which is 9 exabytes and should be more than enough for any one target's LI session. This is also a lot easier to encode and decode, because you have to interpret an INTEGER as though it is a signed value -- this means you need a 72 bit (or larger) integer type to be able to work with the largest supported values nicely if 2^64 -1 is the max value.

If the spec designers had instead picked 2^63 - 1 as the maximum, this problem would go away and be a lot easier to deal with.

</rant>