zebra: Note when the netlink DUMP command is interrupted

zebra: Note when the netlink DUMP command is interrupted

There exists code paths in the linux kernel where a dump command
will be interrupted( I am not sure I understand what this really
means ) and the data sent back from the kernel is wrong or incomplete.

At this point in time I am not 100% certain what should be done, but
let's start noticing that this has happened so we can formulate a plan
or allow the end operator to know bad stuff is a foot at the circle K.

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