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/loadbalance/loadbalance.go

@@ -72,7 +72,7 @@ func roundRobinShuffle(records []dns.RR) {
 			records[0], records[1] = records[1], records[0]
 		}
 	default:
-		for j := 0; j < l; j++ {
+		for j := range l {
 			p := j + (int(dns.Id()) % (l - j))
 			if j == p {
 				continue