Add new rro configuration which can be used to make the p2p dhcp
prefix length larger to reserve the address range outside of leases
subnet prefix length for EAPOL-Key feature. This configuration only
valid if its value larger than dhcp server address prefix length and
config_tether_enable_legacy_wifi_p2p_dedicated_ip is true.
E.g.:leaseSubnetPrefixLength = 25, p2p static address = 192.168.49.1/24
dhcp range: 192.168.49.0 ~ 192.168.49.127 (192.168.49.1/25), reserved
192.168.49.128 ~ 192.168.49.255 for EAPOL-Key feature.
Bug: 170056953
Test: atest TetheringTests
Change-Id: I1319efd871796da7234383a29ab64a1623101ae7
