lint: enable intrange linter (#7331)

Enable intrange linter to enforce modern Go range syntax over
traditional for loops, by converting:

for i := 0; i < n; i++

to:

for i := range n

Adding type conversions where needed for compatibility
with existing uint64 parameters.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/pkg/proxy/connect_test.go

@@ -242,7 +242,7 @@ func TestDial_MultipleCallsAfterStop(t *testing.T) {
 	tr.Stop()
 	time.Sleep(50 * time.Millisecond)
 
-	for i := 0; i < 3; i++ {
+	for i := range 3 {
 		_, _, err := tr.Dial("udp")
 		if err == nil {
 			t.Errorf("Attempt %d: %s: %s", i+1, testMsgExpectedError, testMsgUnexpectedNilError)