eth: conform better to the golint standards (#16783)

* eth: made changes to conform better to the golint standards

* eth: fix comment nit

eth/api_backend.go

@@ -43,6 +43,7 @@ type EthAPIBackend struct {
 	gpo *gasprice.Oracle
 }
 
+// ChainConfig returns the active chain configuration.
 func (b *EthAPIBackend) ChainConfig() *params.ChainConfig {
 	return b.eth.chainConfig
 }