Changing iceCandidatePoolSize to an octet and adding EnforceRange.
Fixes #1048.
Changing it to an octet limits the range to 0-255; there shouldn't be
any situation where an application wants to create thousands of pooled
candidates.
Adding [EnforceRange] means that if the application provides a negative
value or one greater than 255, a TypeError is thrown, rather than the
value being converted to the valid range by doing "mod 256".