net_startmonitor.c always returned zero. In the case where a socket has...

net_startmonitor.c always returned zero.  In the case where a socket has already been closed, it correctly handled the disconnetion event but still returned OK.  Returning OK causes the callers of net_startmonitor to assume that the connection was okay, undoing the good things that net_startmonitor did and causing the socket to be marked as connected.  This behavior was noted by Pelle Windestam.