On RFsimulator end, close open connections
Use the correct function in order to close open RFsim connections, instead of a simple close(). If this is not done correctly, it might happen that the softmodem closes, but an L1 thread might still read samples (bug in higher layers). Then, RFsim tries to read a socket (because it has an open connection), but the actual connection had been close()d. This commit fixes this behavior.
closes #744 (closed)