Function dtrace_enabling_prime

* If an enabling is to be enabled without having matched probes (that is, if * dtrace_state_go() is to be called on the underlying dtrace_state_t), the * enabling must be _primed_ by creating an ECB for every ECB description. * This must be done to assure that we know the number of speculations, the * number of aggregations, the minimum buffer size needed, etc. before we * transition out of D