Initialize NetBlock members.
Clear the sockaddr_in before filling it in.
Set sa_len of IPv4 to sizeof(sockaddr_in), not sizeof(sockaddr_storage).
Have NetBlock::next return the socklen.

This matters on OS X; with the wrong size, connect scans give "Invalid
argument".
Reported by Jesper Kückelhahn.
http://seclists.org/nmap-dev/2013/q1/84
Actually set the base addr in NetBlockIPv6Netmask.

This is needed for proper copying of the scope_id.