zebra: Ensure master's ifname is known, even if slave comes up first

zebra: Ensure master's ifname is known, even if slave comes up first

In if_netlink.c, when an interface structure, ifp, is first created,
its possible for the master to come up after the slave interface does.
This means, the slave interface has no way to display the master's ifname
in show outputs. To fix this, we need to allow creation by ifindex instead
of by ifname so that this issue is handled.

Signed-off-by: Dinesh G Dutt<5016467+ddutt@users.noreply.github.com>