Merge uipc_proto.c:1.26 from HEAD to RELENG_6:

Merge uipc_proto.c:1.26 from HEAD to RELENG_6:

  Remove UNIX domain socket raw socket support.  This feature is documented
  as being undocumented in Stevens, and was broken in 1997 during network
  stack infrastructure work.  It is the one remaining (and incorrect)
  direct protocol reference to raw_usrreq.pru_attach; this is incorrect
  because the raw socket code assumes that raw_uattach is called only after
  the protocol has allocated a PCB.