mxge: There is no need to hold TX serialize to check pkt_done

Since pkt_done is only updated by mxge_tx_done(), which is only called
from the interrupt handler, checking pkt_done from the interrupt handler
does not need TX serialize at all.  This reduce TX serialize contention.
mxge: Make callout on the same CPU which handles interrupt

This avoids main serialize contention
mxge: Remove unused stats
mxge: Remove mlen field from rx ring

This field actually serves no purpose
kernel/drm: Reapply 6d6a80766ccb6c27388c1d0d0db443b0ecd0f2f2