Ncat cannot handle unnamed AF_UNIX sockets

[dmiller-nmap]

Definitely affects SOCK_DGRAM (--udp), but may also have impact on SOCK_STREAM (TCP-style, the default). See http:https://seclists.org/nmap-dev/2014/q4/343 and #23

[t-8ch]

It seems to work with SOCK_STREAM

How should ncat behave if the users want it to send something back?
A warning once if recvonly == false and then ignoring all writes would be fine, or?

[dmiller-nmap]

I believe recent changes (6a9acb1) have resolved this issue. @glicht can you confirm?

[dmiller-nmap]

I am wrong, the issue still exists. The changes I mentioned should make it safe to print debug messages regarding such a connection, but it does not address the issue of calling connect() on such a socket.