ECMP: Addition of new server on ECMP

When a new equal-cost multipath (ECMP) is added dynamically, we avoid complete redistribution of flows. The flows mapped to the existing ECMP remain consistent where only a proportion of the flows are moved to the newly added ECMP. This form of redistribution ensures minimal disruption to the existing ECMP flows and also maintains uniformity in the flow from each active ECMP to the newly added ECMP. The MX Series routers with MPC10, MPC11, LC9600, and MX304 cards support multiple path failures in an ECMP group. This capability prevents reordering of flows to active paths in an ECMP group when one or more paths fail.