It is possible to send so quickly that we start getting EAGAIN on sends.
In listen mode, this means that some sends can get lost. This patch,
adapted from one by Alex Weber, makes sockets blocking for the duration
of the send. This is not as nice as retrying the send through an event
mechanism, but should at least be correct.
http://seclists.org/nmap-dev/2012/q3/670
Compare a similar patch in r13552, which applied to --exec mode.