Switch ServiceModel::ServicePtrRole to some positive int number

Negative role numbers might have worked, but it is not specified if
they are offciailly supported.

With compiler warnings about
    warning: overflow in conversion from 'AdditionalRoles' to 'int'
    changes value from 'ServicePtrRole' to '-1603986978
there is another motivation now to switch to some positive int number
instead, given the ABI can be changed for KF 6.0 now.