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

Move xyz_cxxinitialize.c from nuttx/configs/abc/src to apps/platform/abc/ (where xyz is the processor family and abc is the board)