Our tcp sdn sockets are bidirectional: writing to it should allow *other* side to read, not current side.  Therefore, renamed the existing write method to write_into_read to distinguish it from writing to other side.  Currently breaks a test, which requires a write.  Going to re-add a write for this test.
Allows connecting two manual sdn sockets.  Still need to update a couple of test cases.
Updated test to use new connected sockets.