[bbr] reduce the default reregisteration delay (#7996)
[bbr] reduce the default reregisteration delay (#7996)

After BBR restarting, in order to receive the packets from multicast
group, the devices, which have registered multicast group addresses to
that BBR, needs to re-register these groups. In current logic, the
default max reregistration delay is too large (1200 seconds).
srickardti/openthread,openthread/openthread,openthread/openthread,jwhui/openthread,srickardti/openthread,jwhui/openthread,openthread/openthread,srickardti/openthread,jwhui/openthread,jwhui/openthread,srickardti/openthread,openthread/openthread