Break out separate SCTP tests for half-open sockets.

These should have different behavior than TCP.
http://seclists.org/nmap-dev/2013/q1/227
Quit on EOF in non-TCP mode.

Apparently SCTP can't have the same kind of half-open sockets that TCP
has. When one direction is closed, we can't do anything further with the
socket.
http://seclists.org/nmap-dev/2013/q1/227
XFAIL some tests having to do with EOF handling.

http://seclists.org/nmap-dev/2013/q1/227
Remove a close that made a test unreliable.