Fixes unknown error in usrsctp_connect on Windows. Propagates IOExceptions as an error back to usrsctp stack. Adds transfer test.

SCTP stack will be never deinitialized for the time beign because of the deadlock in usrsctp_finish(). Minor fixes.

Protects against JVM crash when closed SCTP socket is used by checking for null pointer and throwing IOException. Adds unit tests for SCTP wrapper.