First pass at porting John's "accept" changes to

First pass at porting John's "accept" changes to
allow an in-kernel webserver (or similar) to accept
and handle incoming connections using netgraph without ever leaving the
kernel. (allows incoming tunnel requests to be
handled totally within the kernel for example)

Needs work, but shouldn't break existing functionality.

Submitted by:	John Polstra <jdp@polstra.com>
MFC after:	2 weeks