accel-ppp: T5688: Standardized pool configuration in accel-ppp

Standardized pool configuration for all accel-ppp services.

1. Only named pools are used now.
2. Allows all services to use range in x.x.x.x/mask and x.x.x.x-x.x.x.y format
3. next-pool can be used in all services
4. Allows to use in ipoe gw-ip-address without pool configuration which allows to use Fraimed-IP-Address attribute by radius.
5. Default pool name should be explicidly configured with default-pool.
6. In ipoe netmask and range subnet can be different.