* fixed a wrong S-flag handling. * uses TCP-hostcache framework for pMTU discovery in freebsd5,   so that pMTU discovery on TCP works fine.
* fixed a wrong S-flag handling.
* uses TCP-hostcache framework for pMTU discovery in freebsd5,
  so that pMTU discovery on TCP works fine.

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