Fixup interrupting of the ethernet device.

Fixup interrupting of the ethernet device.

dev/ns_gige.cc:
    clean up the interrupt handling code so that it is simpler and
    less prone to bugs.  I hope I removed the bug where the:
    assert(intrTick >= curTick || intrTick == 0); would get triggered.
    I'm pretty sure that was due to intrTick not being cleared when
    the interrupt was cleared.

    This code probably still needs to be looked at more closely to
    make sure interrupts are not missed.

--HG--
extra : convert_revision : 61e2eb043540f2534a80c9b633006a71e7d6e282