Minor refactor of constructor for comparison operator.

Justification: Since the comparison operator is only valid for bytesData, the
constructor should recieve a byte slice as input and then convert it to
registerData. It makes less sense to have the caller create the registerData
from the byte slice if bytes data is the only type of registerData, we accept.

This change removes unnecessary checks and makes the code a lot less wordy by
removing the profuse amount of newBytesData calls for comparison construction.

PiperOrigin-RevId: 670652077

pkg/tcpip/nftables/nftables.go

@@ -638,18 +638,19 @@ func validateComparisonOp(cop cmpOp) error {
 }
 
 // newComparison creates a new Comparison operation.
-func newComparison(sreg uint8, op int, data registerData) (*comparison, error) {
+func newComparison(sreg uint8, op int, data []byte) (*comparison, error) {
 	if sreg == linux.NFT_REG_VERDICT {
 		return nil, fmt.Errorf("comparison operation cannot use verdict register as source")
 	}
-	if err := data.validateRegister(sreg); err != nil {
+	bytesData := newBytesData(data)
+	if err := bytesData.validateRegister(sreg); err != nil {
 		return nil, err
 	}
 	cop := cmpOp(op)
 	if err := validateComparisonOp(cop); err != nil {
 		return nil, err
 	}
-	return &comparison{sreg: sreg, cop: cop, data: data}, nil
+	return &comparison{sreg: sreg, cop: cop, data: bytesData}, nil
 }
 
 // evaluate for Comparison compares the data in the source register to the given
@@ -1003,7 +1004,7 @@ type verdictData struct {
 	data Verdict
 }
 
-// newVerdictData creates a RegisterData for a verdict.
+// newVerdictData creates a registerData for a verdict.
 func newVerdictData(verdict Verdict) registerData { return verdictData{data: verdict} }
 
 // String returns a string representation of the verdict data.
@@ -1044,7 +1045,7 @@ type bytesData struct {
 	data []byte
 }
 
-// newBytesData creates a RegisterData for <= 16 bytes of data.
+// newBytesData creates a registerData for <= 16 bytes of data.
 func newBytesData(bytes []byte) registerData {
 	if len(bytes) == 0 {
 		panic("bytes data cannot be empty")