Added change not to create ECMP Group in SAI and program the route if none of ECMP members are active/link-up

[abdosi]

What I did:
Added change not to create ECMP Group in SAI and program the route if none of the ECMP members are active/link-up.
Also do not program the Temp Route if Neigh is not active (Link Down)

Why I did:
In scale setup of T2 it's possible all links can go down simultaneously which case we can get Route messages with all nexthops being in down state. In such case we might create empty Nexthop Group in SAI for the given route which causes not needed SAI call for Nexthop Group creation and also create traffic blackhole for the route where that route can still forward traffic via default route if eligible/applicable.

Also in this case no point to add Temp Route if neighbor is link down.

How I verify:

1. Compile time test was failing because of this chnage so added oper_status as UP in the mock tests
2. Added UT for this scenario.
3. Ixia Convergence tests

[rlhui]

@prsunny reminder to review, thanks.

[prsunny]

@abdosi , i think the test failures are specific to this PR as I see it passing for all others