Merge branch 'align_key_and_ecdsa_nonce_entropy' of https://github.com/Gustav-Simonsson/go-ethereum into Gustav-Simonsson-align_key_and_ecdsa_nonce_entropy

eth: add default bootnode

* Fixed issues where new peer window could cause a crash when entering
  an empty string

* Sometimes old nonces were set by "old" agents
* Added the hash rate to the miner

For compatibility with cpp-ethereum

udp.Table was assigned after the readLoop started, so
packets could arrive and be processed before the Table was there.

addPeer doesn't allow self connects, but we can avoid opening
connections in the first place.

The deflect logic called Disconnect on the peer, but the peer never ran
and wouldn't process the disconnect request.

There are now two deadlines, frameReadTimeout and payloadReadTimeout.

The frame timeout is longer and allows for connections that are idle.
The message timeout is still short and ensures that we don't get stuck
in the middle of a message.

This deletes the old NAT implementation.

I have verified that UPnP and NAT-PMP work against an older version of
the MiniUPnP daemon running on pfSense. This code is kind of hard to
test automatically.

rlp: add Flat