properly implement the fifo _reserved stuff.

properly implement the fifo _reserved stuff.

dev/pktfifo.cc:
    need to checkpoint _reserved
dev/pktfifo.hh:
    When clearing, clear _reserved
    size() is used for determining how many bytes are in the fifo
    ready to be pulled, so we don't want to add _reserved
    avail() on the other hand is used for determining how much
    free space is in the fifo for adding packets.
    adjust the implementation of empty() and full() to reflect this.

--HG--
extra : convert_revision : 3281972b4b70ea5833d39ae7ce1e73648b3573b0