rng: fix port number range validation

rng: fix port number range validation

The PortNumber data type is declared to derive from 'short'.
Unfortunately this is an signed type, so validates the range
[-32,768, 32,767] which excludes valid port numbers between
32767 and 65535.

We can't use 'unsignedShort', since we need -1 to be a valid
port number too.

This change is to use 'int' and set an explicit max boundary
instead of relying on the data types' built-in max.

One of the existing tests is changed to use a high port number
to validate the schema.

https://bugzilla.redhat.com/show_bug.cgi?id=1214664

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>