Get rid of "forever" loop in the interrupt handler such that we drop out of the interrupt handler if the "Rx Descriptor Unavailable" bit is set and no new mbufs are available to populate descriptors.  Fixes hangs seen with MCLGETI.
Get rid of "forever" loop in the interrupt handler such that we drop out of the
interrupt handler if the "Rx Descriptor Unavailable" bit is set and no new
mbufs are available to populate descriptors.  Fixes hangs seen with MCLGETI.

ok sthen@, deraadt@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars