…an byteBuf.maxCapacity() (netty#16309)

Motivation:

According to the docs of `ByteBuf.maxCapacity()`:

https://github.com/netty/netty/blob/d9336245a2fe3dfec4d0d1e489135bbf7ed03160/buffer/src/main/java/io/netty/buffer/ByteBuf.java#L265-L269

The `byteBuf.capacity()` should always <= `byteBuf.maxCapacity()`.

But if we run the following code:
```
public static void main(String[] args) {
    int maxSize = 100000;
    AdaptiveByteBufAllocator alloc = new AdaptiveByteBufAllocator();
    ByteBuf buf = alloc.newDirectBuffer(maxSize, maxSize);
    System.out.println("Before reallocation: buf.capacity(): " + buf.capacity());
    System.out.println("Before reallocation: buf.maxCapacity(): " + buf.maxCapacity());
    buf = buf.capacity(maxSize + 1); // Should not be allowed.
    System.out.println("After reallocation: buf.capacity(): " + buf.capacity());
    System.out.println("After reallocation: buf.maxCapacity(): " + buf.maxCapacity());
    //assert buf.capacity() <= buf.maxCapacity();
}
```
The output:

> Before reallocation: buf.capacity(): 100000
> Before reallocation: buf.maxCapacity(): 100000
> After reallocation: buf.capacity(): 100001
> After reallocation: buf.maxCapacity(): 100000

We can see after reallocation, the `buf.capacity()` is greater than
`buf.maxCapacity()`, which should not happen.

Modification:

Adjust the check in `AdaptivePoolingAllocator.capacity(int
newCapacity)`, to make sure the constrain hold.

Result:

Make sure `byteBuf.capacity()` not greater than `byteBuf.maxCapacity()`.

---------

Co-authored-by: lao <none>

(cherry picked from commit a78ea77)