babeld: Allow babel to redistribute v6 routes

babeld: Allow babel to redistribute v6 routes

Turn on the ability in babel to receive v6 routes when requested.

robot# show babel route
192.168.201.0/24 metric 0 (exported)
2606:a000:111d:803e::/64 metric 0 (exported)
robot# conf t
robot(config)# int enp3s0
robot(config-if)# ipv6 addr 2404:4000:991d:804c:c32:ee94:742c:4d5/73
robot(config-if)# end
robot# show babel route
192.168.201.0/24 metric 0 (exported)
2606:a000:111d:803e::/64 metric 0 (exported)
2404:4000:991d:804c:c00::/73 metric 0 (exported)
robot#

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