bgpd: associate appropriate family for redistributed connected addresses

bgpd: associate appropriate family for redistributed connected addresses

When redistributing connected addresses, the address family has
to be figured out. The calculation was not done, the next-hop
address length was not set, and as consequence, the nexthop
is displayed like if it was an ipv6 address, which is wrong for
ipv4 addresses.

Calculate the family for connected addresses.
Change the topotests accordingly.

Fixes: ("7226bc40d606") bgpd: ignore NEXT_HOP for MP_REACH_NLRI
Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>