run golangci-lint and apply suggested fixes

rpc/dataconn/frameconn/frameconn.go

@@ -1,7 +1,6 @@
 package frameconn
 
 import (
-	"bufio"
 	"encoding/binary"
 	"errors"
 	"fmt"
@@ -48,7 +47,6 @@ func (f *FrameHeader) Unmarshal(buf []byte) {
 type Conn struct {
 	readMtx, writeMtx sync.Mutex
 	nc                timeoutconn.Conn
-	ncBuf             *bufio.ReadWriter
 	readNextValid     bool
 	readNext          FrameHeader
 	nextReadErr       error

rpc/dataconn/frameconn/frameconn_shutdown_fsm.go

@@ -10,17 +10,11 @@ type shutdownFSM struct {
 type shutdownFSMState uint32
 
 const (
+	// zero value is important
 	shutdownStateOpen shutdownFSMState = iota
 	shutdownStateBegin
 )
 
-func newShutdownFSM() *shutdownFSM {
-	fsm := &shutdownFSM{
-		state: shutdownStateOpen,
-	}
-	return fsm
-}
-
 func (f *shutdownFSM) Begin() (thisCallStartedShutdown bool) {
 	f.mtx.Lock()
 	defer f.mtx.Unlock()