This change unbreaks the build and removes racy access to
disableCheckFreq. Even though the field is set while holding
the lock, it was read outside of the protected section.

For more information about this light client mode, read
https://hackmd.io/s/HJy7jjZpm

Most probably a copy/paste kind of error.
Found with gocritic `dupArg` checker.

TryUpdate does not call t.trie.TryUpdate(key, value) and calls t.trie.TryDelete
instead. The update operation simply deletes the corresponding entry, though
it could retrieve later by odr. However, it adds further network overhead.

This PR enables the indexers to work in light client mode by
downloading a part of these tries (the Merkle proofs of the last
values of the last known section) in order to be able to add new
values and recalculate subsequent hashes. It also adds CHT data to
NodeInfo.

params: fix golint warnings

* all: get rid of error when create mdb

* core: clean up variables definition

* all: inline mdb definition

* core: make current*Block atomic, and accessor functions mutex-free

* core: fix review concerns

* core: fix error in atomic assignment

* core/light: implement atomic getter/setter for headerchain

* les, light: fix CHT trie retrievals

* les, light: minor polishes, test remote CHT retrievals

* les, light: deterministic nodeset rlp, bloombits test skeleton

* les: add an event emission to the les bloombits test

* les: drop dead tester code

This commit reduces database I/O by not writing every state trie to disk.