Disable the KASSERT for curcpu == 0 in netisr for EARLY_AP_STARTUP.

In the EARLY_AP_STARTUP case, thread0 can migrate to another CPU
before this SYSINIT is run. However, the only part of this SYSINIT
that assumes it runs on CPU 0 is in the !EARLY_AP_STARTUP case when it
creates the netisr for the boot CPU. In the EARLY_AP_STARTUP case we
start up the netisr's for the first N CPUs during the SYSINIT itself
and don't depend on running on the boot CPU for correct operation.

This is a direct comit to stable/11 as the assertion was removed as part
of a different change in r302595.

Reported by: rwatson, truckman, jkim, FreeNAS bug 45611