Fix project_network_v6_mask_bits value in case of Contrail env

For contrail env "project_network_v6_cidr = 2003::/120", so we
need to change the "project_network_v6_mask_bits" value from
default '64' up to '124'.

Change-Id: I7a359bdc5a0e50d63982147b5f80dfce4fec729f
Closes-bug: PROD-25897
1 file changed