cleanup interrupt code for gigabit device

cleanup interrupt code for gigabit device

dev/ns_gige.cc:
    Clean up the interrupt code.  Do a better job determining when
    coalescing should happen.
    Remove some bogus comments
    Stop using magic numbers in initialization and comment what
    the various numbers do
dev/ns_gige_reg.h:
    #define describing which interrupts cannot be delayed and
    which interrrupts we don't implement

--HG--
extra : convert_revision : eb196afa0bf448e1849dd2bd30dde32134effee7