The tcp_open_active() and tcp_open_passive() functions don't really have
any strong dependencies on TCP. With a couple of simple changes they
can be used for UDP also. Since this is useful for Netflow, this commit
does so.
The TCP and SSL vconn implementations had a lot of common code to make
and accept TCP connections, which this commit factors out into common
functions in socket-util.c.
Also adds the ability to bind ptcp and pssl vconns to a particular IP
address instead of the wildcard address.
