PX4 uses NuttX data structures throughout so those data structures
were preserved and used to implement high and low priority queues.
A unit test for the work queues was added.
The polling rate of the queues are set in px4_config.h in
CONFIG_SCHED_WORKPERIOD. The units are milliseconds.
Signed-off-by: Mark Charlebois <charlebm@gmail.com>
