Transaction unindexing will be enabled by default as of 1.10, which causes tx status retrieval will be broken without this PR. 

This PR introduces a retry mechanism in TxStatus retrieval.

This PR adds a more CLI flag, so that the les-server can serve light clients even the local node is not synced yet.

This functionality is needed in some testing environments(e.g. hive). After launching the les server, no more blocks will be imported so the node is always marked as "non-synced".

eth/protocols/snap: lower abortion and resumption logs to debug

This removes support for all deprecated flags except --rpc*.

travis: bump builders to Bionic

travis: bump Android NDK version

cmd/utils: disable caching preimages by default

* travis, appveyor, build: bump Go to 1.16

* accounts/abi/bind: fix up Go mod files for Go 1.16

This PR prevents users from submitting transactions without EIP-155 enabled. This behaviour can be overridden by specifying the flag --rpc.allow-unprotected-txs=true. 

This PR introduces:

- db.put to put a value into the database
- db.get to read a value from the database
- db.delete to delete a value from the database
- db.stats to check compaction info from the database
- db.compact to trigger a db compaction

It also moves inspectdb to db.inspect.

* les: refactored server handler

* tests/fuzzers/les: add fuzzer for les server handler

* tests, les: update les fuzzer

tests: update les fuzzer

tests/fuzzer/les: release resources

tests/fuzzer/les: pre-initialize all resources

* les: refactored server handler and fuzzer

Co-authored-by: rjl493456442 <garyrong0905@gmail.com>

* les/lespay/server: fix balance expiration and add test

* les: move client balances to a new db

* les: rename lespayDb to lesDb

In the random sync algorithm used by the DNS node iterator, we first pick a random
tree and then perform one sync action on that tree. This happens in a loop until any
node is found. If no trees contain any nodes, the iterator will enter a hot loop spinning
at 100% CPU.

The fix is complicated. The iterator now checks if a meaningful sync action can
be performed on any tree. If there is nothing to do, it waits for the next root record
recheck time to arrive and then tries again.

Fixes #22306

* eth/protocols/eth: split up the eth protocol handlers

* eth/protocols/eth: define eth-66 protocol messages

* eth/protocols/eth: poc implement getblockheaders on eth/66

* eth/protocols/eth: implement remaining eth-66 handlers

* eth/protocols: define handler map for eth 66

* eth/downloader: use protocol constants from eth package

* eth/protocols/eth: add ETH66 capability

* eth/downloader: tests for eth66

* eth/downloader: fix error in tests

* eth/protocols/eth: use eth66 for outgoing requests

* eth/protocols/eth: remove unused error type

* eth/protocols/eth: define protocol length

* eth/protocols/eth: fix pooled tx over eth66

* protocols/eth/handlers: revert behavioural change which caused tests to fail

* eth/downloader: fix failing test

* eth/protocols/eth: add testcases + fix flaw with header requests

* eth/protocols: change comments

* eth/protocols/eth: review fixes + fixed flaw in RequestOneHeader

* eth/protocols: documentation

* eth/protocols/eth: review concerns about types

io.Reader may return n > 0 and io.EOF at the end of the input stream.
readFull did not handle this correctly, looking only at the error. This fixes
it to check for n == len(buf) as well.

* core/state: copy the snap when copying the state

* core/state: deep-copy snap stuff during state Copy

This PR optimizes the broadcast loop. Instead of iterating twice through a given set of transactions to weed out which peers have and which do not have a tx, to send/announce transactions, we do it only once.

eth: fix snap sync cancellation

This updates the eth protocol test suite to use the message type
definitions of the 'production' protocol implementation in eth/protocols/eth.

core/state/snapshot: ensure Cap retains a min number of layers

trie: fix bloom crash on fast sync restart

Make geth build on FreeBSD, fixes #22309.

core: fix temp memory blowup caused by defers holding on to state