- recovered all the flag bits in pkthdr.csum_flags for ip_fragment to   calculate checksum correctly.  pkthdr.csum will be fixed again   in ip_fragment. - moved the consideration for the case of CSUM_DELAY_DATA && !CSUM_IP_FRAGS   to ip_fragment().  this should be here since ip_fragment() can also be   called from a pf routine.
- recovered all the flag bits in pkthdr.csum_flags for ip_fragment to
  calculate checksum correctly.  pkthdr.csum will be fixed again
  in ip_fragment.
- moved the consideration for the case of CSUM_DELAY_DATA && !CSUM_IP_FRAGS
  to ip_fragment().  this should be here since ip_fragment() can also be
  called from a pf routine.

MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame