add support for DNS Search List (rfc6106)

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
ndptool: push litefime printout into separete function

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
add man page for ndptool

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
add missing list.h into Makefile.am

Signed-off-by: Jiri Pirko <jiri@resnulli.us>