ECMP only supports previously configured/learned next-hops

[rubensfig]

Expected Behavior

The routes should be configured on the switch, even though the next hops are not learned.

Actual Behavior

Route is not configured on the switch, even after next-hop resolution. Leads to a break in kernel-switch state.

Steps to Reproduce the Problem

Configure the following route, while not having any nexthop.

ip route add $ECMP_ROUTE nexthop via $NEIX weight 1 nexthop via $NEIY weight 2