Unix domain:  Enable logic to clean up the FIFOs underlying stream sockets with those sockets are disconnected.  Tehre is still no corresponding clean-up logic in place for Unix domain datagram sockets because the life of the FIFO is not as well known in that case

Tiva Ethernet: Integrate use of workqueue so the network processing is not done at the interrupt level

Add support for a variadic ioctl() function.  The ioctl() interface is a non-standard, Unix interface.  NuttX has always used the older, three-parameter version.  Most contemporary systems now, however, use a variadic form of the ioctl() function.  Added an option to insert a shim layer to adapt the three-parameter ioctl() to use the variadic interface form.  Internally, the ioctl handling is the same three-parameter logic.  The only real complexity to the shim is in how the system calls must be handled.

The Asynch I/O implementation now satisfies POSIX priority requirements; it uses the new low priority worker thread interfaces to adjust the priority of the worker thread according to the priority of the client thread