zebra: Add a dump table information command to zebra

zebra: Add a dump table information command to zebra

Allow zebra to dump the table information it has from a router perspective.

This table looks like this:
donna.cumulusnetworks.com# show zebra router table summary
VRF             NS ID    VRF ID     AFI            SAFI    Table      Count
---------------------------------------------------------------------------
default             0         0    IPv4         unicast       49          1
default             0         0    IPv4         unicast      254          7
default             0         0    IPv4       multicast      254          9
default             0         0    IPv6         unicast      254          1
default             0         0    IPv6       multicast      254          1
BLUE                0        31    IPv4         unicast     1005          0
BLUE                0        31    IPv4       multicast     1005          0
BLUE                0        31    IPv6         unicast     1005          0
BLUE                0        31    IPv6       multicast     1005          0

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