Add a simple test of the scheduler instrumentation logic.  This initial version is still kind of buggy.

apps/modbus/nuttx/portserial.c:  Was not returning an error on failure to open the device driver.  From Olololshka kokoko

UAVCAN: Add a patch to make the verified version of UAVCAN compatible with the current NuttX code base

apps/: Replace irqsave() with enter_critical_section(); replace irqrestore() with leave_critical_section()

DHCPD no longer calls directly into the OS, but uses network IOCTL commands to modify the ARP table.

Low level drive access functions should not generate output; it interferes with higher level formatting