namespace: add source file location exceptions

Teach namespace checker about some special case files where the
source is in unusual location.  This fixes many of the source file
not found errors (more can be added), and also prevents false positives
for functions not being used.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>