lib: Differentiate between real and cpu bound processes

lib: Differentiate between real and cpu bound processes

When generating SLOW_THREAD warnings let's differentiate between
a cpu bound process and a wall bound process.  Effectively
a slow thread can now be a process in FRR doing lots of work( cpu bound )
or wall bound ( the cpu is heavy load and a FRR process may be pre-empted
and never scheduled ).

Signed-off-by: Donald Sharp <sharpd@nvidia.com>