Activating SRRP state tracking

The SRRP state tracking by routes is turned on only when needed.

For subscriber-interface routes (IPv4 and IPv6), this is performed explicitly.

subscriber-interface <ip-int-name>
    address <ip-address> gw-ip-address <gw-address> track-srrp <inst-name> holdup-
time <msec> 
        ipv6
        subscriber-prefixes
            prefix <ipv6-prefix> pd track-srrp <srrp-id> holdup-time <msec>
            prefix <ipv6-prefix> wan-host track-srrp <srrp-id> holdup-time <msec>

For managed and subscriber management routes, this is explicitly enabled under the group interface:

group-interface <ip-int-name>
    srrp-enabled-routing holdup-time <msec>