zebra: On linux let interface data come in through netlink messaging

zebra: On linux let interface data come in through netlink messaging

Consolidate on linux to using the netlink api for gathering all data
about a interface.  Leave this interface alone in the meantime for
other OS's.

This also has the side effect of reducing the amount of work
being done on linux in that FRR was handling shut/no shut
events 2 times.  Once for the ioctl question asked and
once for the netlink message received.

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