Set target port number based on target af, not o.af.

o.af is AF_UNSPEC at this point in the common case that neither -4 nor
-6 was given. The code was falling through to the "else" IPv6 case. I
think we were getting luck with this because the port number happens to
be in the same place in sockaddr_in and sockaddr_in6.

ncat/ncat_main.c

@@ -639,7 +639,7 @@ int main(int argc, char *argv[])
         o.portno = (unsigned short) long_port;
     }
 
-    if (o.af == AF_INET)
+    if (targetss.storage.ss_family == AF_INET)
         targetss.in.sin_port = htons(o.portno);
 #ifdef HAVE_IPV6
     else