Call long as l instead of i (netty#10578)

Motivation:

Long should be called `l` instead of `i` because `i` is generally used for `int`.

Modification:

Changed `i` to `l`.

Result:
Better naming

common/src/main/java/io/netty/util/internal/ObjectUtil.java

@@ -50,11 +50,11 @@ public static int checkPositive(int i, String name) {
      * Checks that the given argument is strictly positive. If it is not, throws {@link IllegalArgumentException}.
      * Otherwise, returns the argument.
      */
-    public static long checkPositive(long i, String name) {
-        if (i <= 0) {
-            throw new IllegalArgumentException(name + ": " + i + " (expected: > 0)");
+    public static long checkPositive(long l, String name) {
+        if (l <= 0) {
+            throw new IllegalArgumentException(name + ": " + l + " (expected: > 0)");
         }
-        return i;
+        return l;
     }
 
     /**
@@ -72,11 +72,11 @@ public static int checkPositiveOrZero(int i, String name) {
      * Checks that the given argument is positive or zero. If it is not, throws {@link IllegalArgumentException}.
      * Otherwise, returns the argument.
      */
-    public static long checkPositiveOrZero(long i, String name) {
-        if (i < 0) {
-            throw new IllegalArgumentException(name + ": " + i + " (expected: >= 0)");
+    public static long checkPositiveOrZero(long l, String name) {
+        if (l < 0) {
+            throw new IllegalArgumentException(name + ": " + l + " (expected: >= 0)");
         }
-        return i;
+        return l;
     }
 
     /**