* node: expose config in service context
* eth: integrate p2p/dnsdisc
* cmd/geth: add some DNS flags
* eth: remove DNS URLs
* cmd/utils: configure DNS names for testnets
* params: update DNS URLs
* cmd/geth: configure mainnet DNS
* cmd/utils: rename DNS flag and fix flag processing
* cmd/utils: remove debug print
* node: fix test
This commit affects p2p/discv5 "topic discovery" by running it on
the same UDP port where the old discovery works. This is realized
by giving an "unhandled" packet channel to the old v4 discovery
packet handler where all invalid packets are sent. These packets
are then processed by v5. v5 packets are always invalid when
interpreted by v4 and vice versa. This is ensured by adding one
to the first byte of the packet hash in v5 packets.
DiscoveryV5Bootnodes is also changed to point to new bootnodes
that are implementing the changed packet format with modified
hash. Existing and new v5 bootnodes are both running on different
ports ATM.
